Altanbaatar, Battushig

Hanžl P., Janoušek V., Hrdličková K., Buriánek D., Gerel O., Altanbaatar B., Hora J.M., Čoupek P.

Chimeddorj B., Munkhbat D., Altanbaatar B., Dolgorjav O., Oyuntsetseg B.

This study determines the properties of hot spring waters and associated rocks, calculates reservoir temperatures and depths in the Mongolian Altai region, and constructs a conceptual model for geothermal water based on these results. The hot springs consist of HCO 3 -Na, SO 4 -Na, and HCO 3 -SO 4 -Na mixed type waters. The waters exhibit alkaline pH levels and temperatures in the range of 21.3–35°C. X-ray diffraction analyses of outcrop rocks reveal silicate and carbonate-type minerals such as quartz, albite, orthoclase, dolomite, mica, and actinolite, while correlation analysis indicates that the chemical composition of the hot spring water is directly related to rock mineral composition. Dissolution of albite, orthoclase, and dolomite minerals has played an important role in the chemical composition of the waters. Reservoir water circulation depths were 2615–3410 m according to quartz and chalcedony geothermometry. The results indicate that the spring water in the Mongolian Altai region comprises a low mineral content with alkaline pH levels and the reservoir temperature can reach up to 106°C. We also propose a conceptual model for geothermal water in the Chikhertei hot spring. The geothermal water in the Mongolian Altai region exhibits a potential for use in heating systems. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Míková J., Zavřelová A., Hanžl P., Battushig A., Hrdličková K.

A new occurrence of Permian volcanic and volcaniclastic rocks in the Mongolian Altai south of the Main Mongolian Lineament was described between soums of Tugrug and Tseel in Gobi-Altai aimag. Studied vitrophyric pyroxene basalt lies in a layer of agglomerate and amygdaloidal lavas, which is a part of NE–SW trending subvertical sequence of varicolored siltstones and volcaniclastic rocks in the Tsengel River valley. This high-Mg basalt is enriched in large ion lithophile elements, Pb and Sr and depleted in Nb and Ta. LA-ICP-MS dating on 44 spots reveals several concordia clusters. The whole rock geochemistry of sample fits volcanic arc characteristic in the geotectonic discrimination diagrams. Dominant zircon data yield Upper Carboniferous and Permian magmatic ages 304.4 ± 2.3 and 288.6 ± 1.9 Ma. Two smaller clusters of Upper Devonian (376 ± 4.7 Ma) to Lower Carboniferous ages (351.9 ± 3.5 Ma) indicate probably contamination of ascending magmatic material. Youngest Triassic age found in three morphologically differing grains reflects probably lead loss. Described high-Mg basalt lava represents sub-aerial volcanism in volcanic arc environment developed over the N dipping subduction zone in the southwestern Mongolia in the time span from Uppermost Carboniferous to Permian during terminal stage of its activity.

Hanžl P., Guy A., Battushig A., Lexa O., Schulmann K., Kunceová E., Hrdličková K., Janoušek V., Buriánek D., Krejčí Z., Jiang Y., Otgonbaatar D.

The geological map L-47-V at a scale 1:500,000 covers part of Mongolian Altaids with ophiolite fragments in southern Central Asian Orogenic Belt in SW Mongolia. This region has a basin and range to...

Sodov A., Gaskova O., Gankhuyag A., Lkhagvasuren D., Dorjsuren O., Tumen-Ulzii O., Altanbaatar B.

The Khangay-Khentey belt is located in central Mongolia (Central Asian Orogenic Belt). The Uyanga ore knot district of the Khangay metallogenic zone are hosted by the lower-middle Devonian volcanogenic-sedimentaryErdenetsogtformation. The new Burgetei, Ult and Senjit gold occurrences were studied. The rocks of theErdenetsogtformation have an irregular gold content: 0.96 g/t Au is determined in quartz vein (BG-7/16), Au content is highest up to 3.5 g/t in the quartzite-jasper (Ult-7/16 and Ult-9/16) cut by quartz veins in the Ult occurrence. The Senjit occurrence represents Au-Hg-Sb epizonal level of orogenic gold deposits structure with highest Hgand Sb content up to 8.5 ppm and 39 ppm respectively. The Au content of arsenic pyrite of the Burgetei and Ult is below the detection limit by electron microprobe analysis. The Au content of arsenopyrite of the Ult occurrence is highest (up to 238 ppm). The ore-mineral assemblages in the new gold occurrences reflect the differences between three explored sites, formed in the course of fluid evolution during the water-rock interaction. Variable concentrations of indicative elements (As, Te, Sb, Hg) and their ratios confirm this fact.

Nguyen H., Hanžl P., Janoušek V., Schulmann K., Ulrich M., Jiang Y., Lexa O., Altanbaatar B., Deiller P.

Baaran and Baytag “terranes” form important part of the Trans-Altai Zone of the Central Asian Orogenic Belt in the SW Mongolia. The Trans-Altai Zone represents an oceanic domain built by Ordovician to Devonian ophiolites covered by Devonian–Carboniferous oceanic sediments. This oceanic assemblage was intruded by a spectrum of Carboniferous volcanic rocks ranging from basalts to rhyolites (325.6 ± 1.4 Ma to 351.0 ± 5.9 Ma; LA-ICP-MS U–Pb dating on zircon) that display similar whole-rock trace-element and Sr–Nd isotopic signatures regardless their silica contents and the “terrane” they belong to. They are normal-K calc-alkaline rocks whose NMORB-normalized multielement patterns show an arc-like enrichment in LILE (Large Ion Lithophile Elements) and deep negative TNT (Ta, Nb, Ti) anomalies. Based on the relatively high Nb/Yb and Th/Yb ratios, the arc was probably formed on immature continental rather than typical oceanic crust. Low (87Sr/86Sr)i (0.7043–0.7047), high e Nd 350 (+5.2 to = +5.8) and the observed in-situ Hf isotopic variation in dated zircons ( e Hf t  = +7.4 to +13) are all attributed to a partial melting of primitive and youthful (Neoproterozoic–Ordovician) arc-type lower continental crust (metamorphosed intermediate–acid igneous rocks and/or arc-derived greywackes), augmented with, and most likely facilitated by, contemporaneous arc-related basaltic intrusions. A distinct possibility remains the previously formulated model assuming that the Carboniferous magmatism in Gobi-Altai and Trans-Altai zones sampled the juvenile Neoproterozoic to Cambrian arc crust relaminated under the Ordovician–Devonian oceanic crust. In any case, the studied arc association, together with lithological sequence of ophiolites, can be closely correlated with the Dulate arc in eastern Junggar. It is proposed that the two arc sequences form a single belt, c. 500 km long, that represents one of the main known arc structures in the Central Asian Orogenic Belt.

Janoušek V., Jiang Y., Buriánek D., Schulmann K., Hanžl P., Soejono I., Kröner A., Altanbaatar B., Erban V., Lexa O., Ganchuluun T., Košler J.

The Khantaishir Magmatic Complex (KMC) (south–central Mongolia) exposes a section of a magmatic system consisting of deep crustal, ultramafic cumulates (coarse-grained Amp gabbros and hornblendites; c. 0.35–0.5 GPa) to shallower crustal levels dominated by Amp–Bt tonalites ( c. 0.1–0.2 GPa). The magmatic rocks were emplaced during most of the Cambrian ( c. 538–495 Ma) and are mostly geochemically primitive (Mg# ~ 50), Na-rich and metaluminous. The (normal-) calc-alkaline signature and characteristic trace-element enrichment in hydrous-fluid mobile large-ion lithophile elements (LILE) relative to high-field strength elements (HFSE) suggest an origin within a magmatic arc. Multiple intrusions of basic magma derived from a subduction-modified depleted mantle developed by fractional crystallization and/or accumulation of (Ol, Cpx) Amp + Bt, later joined by Pl. Magma mixing with, or without, exchange of xenocrysts between compositionally dissimilar melt batches was also important. Over time, partial melting of older, lower crustal metabasic rocks became increasingly significant, again with a strong subduction signature. The lack of zircon inheritance in the magmatic products and rather high zircon e Hf t values (all >+3, but for most samples > +8) as well as whole-rock Sr–Nd isotopic compositions imply that the arc was not founded on mature continental crust. It was probably located at the margin of the Baydrag microcontinent, dominated by accreted metabasic rocks of an older (early Tonian?) island arc covered by a thin layer of subordinate metasediments containing detrital zircons with Tonian and ill-defined Palaeoproterozoic ages. The KMC represents a small vestige of an extensive Cambrian–Ordovician subduction system (termed here the Ikh-Mongol Arc System), bordering the western margin of a chain of Precambrian microcontinents (Tuva-Mongolia, Zabkhan and Baydrag) that, together with accreted Neoproterozoic marginal basins (the Lake Zone), defines the external part of the Mongolian orocline.

Hanžl P., Krejčí Z., Altanbaatar B., Lexa O., Buriánek D., Janoušek V., Schulmann K., Jiang Y., Hrdličková K.

ABSTRACTA geological map is an indispensable tool for understanding the structure of the Earth’s crust but high-quality geological maps are usually lacking in remote areas of mountainous Central Asia covered by vast deserts. The progress in remote sensing and geographical information system (GIS), as well as the advancement in analytical methods, have generated new challenges in producing modern geological maps in such regions. The presented 1:50,000 geological map along the Sagsai River summarizes new and more accurate geological data from the geologically interesting region at the contact of the supracrustal and deep crustal Tugrug and Tseel units forming the metamorphosed accretionary wedge on the S and SW slopes of the Mongolian Altai. These geological units are formed by the lower Palaeozoic volcano-sedimentary sequences affected by Devonian Barrovian metamorphism ranging from lower greenschist to granulite facies. This metamorphic basement was subsequently intruded by the post-orogenic late Carbonif...

Ariunbileg S., Gaskova O., Vladimirov A., Battushig A., Moroz E.

In the Dornogobi Aimag region of Southern Mongolia, the main source of groundwater contamination by U, As, and Se is hydrogenic- or sandstone-type uranium deposits. These environmentally hazardous deposits, located in close proximity to populated settlements, pose a serious threat to drinking water quality and human health. Fifty samples were analyzed and levels of uranium were found to be elevated in deep and shallow waters (200 and 34.7 μg/L, respectively), with nearly 25% exceeding the World Health Organization (WHO) guideline level for drinking water quality (30 μg/L). Local rocks and soils appear to be the natural source of uranium. In particular, water from deep hydrologic wells near the largest deposits (Dulaan Uul and Zoovch Ovoo) exceeds the WHO guideline levels for U, As, Se, Sb, Cd, and Fe. At the same time, shallow groundwater (Argalant area) contains 50.5 μg/L of As, 34.7 μg/L of U, and 35.9 μg/L of Cd. Although multiple metal and metalloid contamination of groundwater is an issue of global concern, our understanding of the physical-chemical conditions of its accumulation is limited. This study provides a plausible explanation of the geochemical situation at the uranium Dornogobi province based on thermodynamic calculations.

Buriánek D., Janoušek V., Hanžl P., Jiang Y., Schulmann K., Lexa O., Altanbaatar B.

Hanžl P., Schulmann K., Janoušek V., Lexa O., Hrdličková K., Jiang Y., Buriánek D., Altanbaatar B., Ganchuluun T., Erban V.

Soejono I., Collett S., Schulmann K., Štípská P., Míková J., Peřestý V., Novotná N., Guy A.

Liao Y., Zhang W., Rong Y., Li L., Hu G.

Peřestý V., Soejono I., Schulmann K., Ruffet G., Kylander‐Clark A., Sláma J., Štípská P., Maierová P., Hanžl P., Aguilar C., Kašpar A.

AbstractStructural analysis, U–Pb monazite and xenotime dating, Ar–Ar dating of biotite and amphibole and thermodynamic modeling of peak metamorphic assemblages allow constraining the tectono‐thermal evolution of the migmatite‐magmatite domain on the southern periphery of Precambrian Zavkhan Block. The main subvertical metamorphic fabric resulted from upright folding and almost complete transposition of early sub‐horizontal foliation of uncertain age. P–T conditions of 760–790°C at 0.7–0.8 GPa and in situ U–Pb metamorphic monazite 505–495 Ma ages characterize this tectono‐metamorphic event. It was associated with syn‐deformational partial melting and intrusion of axial planar syntectonic leucogranite veins. Monazite and xenotime from these veins give U–Pb age of c. 500 Ma, confirming that the migmatization and formation of subvertical fabric were coeval. Such time constraints are contemporaneous with ages of gneissified Ikh‐Mongol Arc granite sheets intruding horizontally shortened partially molten crust thereby confirming syn‐compressional nature of arc emplacement. Thermal modeling of cooling history of the whole migmatite‐magmatite domain constrained by Ar–Ar ages is compatible with the shortening of the hot system followed by moderate erosion. The P–T and geochronological data of the Zavkhan block margin are almost identical to those of short lived late Cambrian magmatism and metamorphism described in the Khondalite belt in Far East China and in other places of Mongolian Collage suggesting that these two domains may have formed a continuous belt.

Batkhuyag E., Tserendash N., Tumen-Ulzii O., Tong Y., Lei G., Khurelbaatar U., Garvaa B.

Abstract In this paper, we present the new results of the U–Pb age dating and Lu-Hf isotopic analysis of detrital zircons of the four representative metasedimentary rock samples from the Mongol Altai Group, Mongolian part of the Altai-Mongolian terrane. Our new results indicate that the metasedimentary rocks of the Mongol Altai Group were formed after ∼497 Ma, Late Cambrian and deposited during the Early-Middle Ordovician. The detrital zircons of four samples yield a two major age peaks at 503–517 Ma, and 775–843 Ma, respectively, with minor involvement of older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of Early Paleozoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement. With combination of previous studies in the Chinese Altai, Russian Altai and Hovd terrane, our data suggest that the Altai–Mongolian terrane possibly represents a coherent continental arc-accretionary prism system built upon the active margin of the western Mongolia during the Cambrian to Ordovician. Moreover, the dominant Neoproterozoic to Early Paleozoic detrital zircons from the Mongol Altai sequence yield largely varied εHf(t) values from −17.4 to +12.0, indicating that input juvenile material and reworking of crustal components are both important in the accretionary orogenesis. A compilation of U–Pb and Hf isotope data of detrital zircons shows that the source area underwent two most extensive magmatic activities at ca. 470–574 Ma and 687–967 Ma, respectively.

Kumladze R.M., Tielidze L.G., Gamkrelidze M., Cook S.J., Giorgadze A.

Geological mapping provides vital information about the structure, evolution, natural resource potential, and geohazards of a specific area. The role of geological mapping is especially valuable for mountainous countries like Georgia. In this context, we present a geological map of the Mulkhura River Valley in the Georgian Caucasus (43°3′ N, 42°52′ E) with accompanying cross-sections at a scale of 1:30,000, covering approximately 220 km2. The geological information in the map is based on a comprehensive review of previously published geological maps and literature, combined with original analysis of satellite imagery and hitherto unpublished field data. The extensive spatial coverage and accompanying cross-sections provide detailed insights into the structure of the region. This new map will serve as a foundation for future geological research, hazard management, and resource exploration in the area, as well as for geoconservation to develop the national geotourism industry in this region.

Soldner J., Schulmann K., Štípská P., Jiang Y.

In the Mongolian Collage, metamorphic pressure–temperature ( P – T ) and timing reveal a one-stage evolution defined by a duality of late Neoproterozoic–Ordovician subduction-related low T / P metamorphism and suprasubduction high T / P metamorphism recorded in the Mongolia–Manchuria and Baikal–Sayan belts. This was followed by gradual prevalence of suprasubduction high T / P metamorphism towards the late Paleozoic corresponding to the Altai and South Altai cycles. In the Tarim–North China Collage, metamorphic P – T and timing reveal a two-stage evolution, from dominant intermediate T / P metamorphism possibly resulting from Ordovician–Devonian amalgamation and Andean-type evolution of the collage, to dual low and high T / P metamorphism in the Carboniferous–Permian reflecting subduction–collision processes along the South Tianshan suture in the west and a suprasubduction evolution along the Solonker suture in the east. Altogether, the Paleozoic tectonometamorphic evolution of the two collages in the Central Asian Orogenic Belt shows remarkable differences, with the Mongolian Collage displaying features typical of peripheral accretionary style reflecting recurrent tectonic switches that can be regarded as a single orogenic system, and a two-stage evolution of the Tarim–North China Collage with features of both peripheral–accretionary and interior–collisional orogenic cycles, but mostly related to recurrent subductions of interior oceans.

Wang J., Feng W., Lu J., Wu J., Cao W., Zhang J., Zhang C., Hu B., Li W.

AbstractExcessive Fe2+ in coastal aquaculture source water will seriously affect the aquaculture development. This study used manganese sand to investigate the removal potential and mechanism of Fe2+ in coastal aquaculture source water by column experiments. The pseudo‐first‐order kinetic model could better describe Fe2+ removal process with R2 in the range of 0.9451–0.9911. More than 99.7% of Fe2+ could be removed within 120 min while the removal rate (k) was positively affected by low initial concentration of Fe2+, high temperature, and low pH. Logistic growth (S‐shaped growth) model could better fit the concentration variation of Fe2+ in the effluent of the column (R2>0.99). The Fe2 breakthrough curve could be fitted by Bohart‐Adams, Yoon‐Nelson, and Thomas models (R2>0.95). Smooth slices with irregular shapes existed on the surface of manganese sand after the reaction while Fe content increased significantly on the surface of manganese sand after the column experiment. Moreover, FeO (OH) was mainly formed on the surface of manganese sand after the reaction.Practitioner Points Fe2+ in coastal aquaculture source water could be removed by manganese ores. The pseudo‐first‐order kinetic model better described the Fe2+ removal process. FeO (OH) was mainly formed on the surface of manganese sand after the reaction.

Longfei Xu, Chen S., Zhang J., Cheng Y., Li Q., Chen L., Sun Y., Tan H.

Geothermal Resource as a kind of renewable energy is widely distributed in tectonically active regions. Using hot springs along the Red River fault zone as an example, this study attempts to analyze the recharge source, recharge elevation, reservoir temperature, circulation depth, mixing of cold groundwater, and heat source through ions, stable hydrogen and oxygen isotopes, and data in previous studies to determine the characteristics and formation mechanism of geothermal resources in tectonically active regions. The findings show that whereas the non-thermal groundwater is abundant in $${\text{HCO}}_{3}^{ - }$$ –Ca2+, the hot springs in the Red River Fault are predominantly of the $${\text{HCO}}_{3}^{ - }$$ –Na+ type. The stable hydrogen and oxygen isotopes indicate that the geothermal water is derived from local meteoric precipitation, with a positive excursion in the oxygen isotope indicating that the geothermal water has undergone the strong water-rock interaction under high reservoir temperature. The recharge area is located in the mountainous regions on both sides of the Red River Fault, with recharge elevations ranging from 2252 and 3482 m. The reservoir temperature varies from 67.4 to 173.42°C calculated by the SiO2 geothermometer, and the associated circulation depth is between 1601.18–5134.12 m. Furthermore, the data of previous studies suggest that the primary heat sources in the study area are mantle-derived heat, crust-derived heat, and radioactive heat, while the composition ratio of various heat sources is different from north to south because of the influence of structural development. The primary determinants of geothermal resources in tectonically active regions are the composition of the heat source and the scale and number of large faults, which in turn affect the temperature of geothermal resources.

Sukhbaatar T., Schulmann K., Janoušek V., Soejono I., Lexa O., Míková J., Hora J.M., Song D., Xiao W., Poujol M., Onongoo T., Dashdorjgochoo O., Zeng H.

Geochronological and geochemical investigation of the magmatic and sedimentary rocks from the south-eastern tip of the Bayankhongor Zone (central Mongolia) constrains the Neoproterozoic evolution of the northern margin of the Baidrag Block. There, ultramafic to felsic igneous rocks of the Khan-Uul Massif intruded the volcano-sedimentary sequence of the Ulziit Gol Unit. U–Pb zircon ages show that both the plutonic and volcanic rocks were coeval products of the same Ediacaran (598–564 Ma) magmatism. Most of the samples have low contents of high field strength elements typical of arc-related magmas; however, some mafic rock samples display N-MORB-like chemistry. Magmatic rocks in the Khan-Uul Massif and Ulziit Gol Unit yielded exclusively positive initial εHf in zircon values (+4.9 to +13.8), implying derivation from depleted-mantle sources. Furthermore, heterogeneity of the whole-rock initial εNd values (–4.0 to +2.1) documents that fractional crystallization was accompanied by variable crustal contamination. The detrital zircon age patterns of the sandstone and tuffites in the Ulziit Gol Unit indicate that the sequence was filled dominantly by Ediacaran magmatic detritus derived from the Khan-Uul Massif and its volcanic equivalents, while the older cratonic material from the Baidrag basement represented only a subordinate component. Combined magmatic and sedimentary records imply that both the Khan-Uul Massif and the Ulziit Gol Unit may have formed in the same back-arc basin environment. This challenges the previous view that the entire Bayankhongor Zone was ophiolitic in nature. Distribution of coeval Ediacaran supra-subduction systems on the scale of the Mongolian Collage indicates the closure of multiple oceanic basins rimming the Siberian Continent. Following Rodinia break-up, this peri-Siberian realm was presumably formed by sub-parallel continental ribbons and oceanic basins. It is proposed that the amalgamation of these blocks and closure of intervening oceans reflected the Ediacaran advancing mode of the Palaeo-Pacific subduction.

Zhang B., Yan T., Wang X., Qiao Y., Liu H., Zhang B.

Papadopoulou M., Barry T.L., Dash B., Halton A.M., Sherlock S.C., Hunt A.C.

Since the closure of the Mongol-Okhotsk Ocean in the Mesozoic, Mongolia has been in an intraplate tectonic setting; the nearest plate boundary being ∼3,000 km to the east, at the active Pacific subduction front. Throughout this time, Mongolia has experienced magmatism in the form of distinctive, small-volume volcanic fields dispersed along the central and eastern parts of the country. On the basis of geochemical, isotopic, palaeomagnetic and zircon data, the magmatism can be discriminated from preceding post-collisional magmatism. Gradual change from a lithospheric to an asthenospheric mantle source suggests lithospheric delamination occurred beneath Mongolia, starting at ∼140 Ma and terminating at ∼107 Ma. Accordingly, the onset of intraplate magmatism is set at 107 Ma. Regardless of the spatial and temporal occurrence and evolution of the intraplate magmatism in Mongolia, the geochemistry of the resultant volcanic rocks throughout time remains remarkably similar, although the cause of magmatism has been much debated. Through evaluation of available K-Ar and Ar-Ar data from the literature, along with newly-obtained data from three different volcanic fields, we have identified that the intraplate volcanism in Mongolia has been near-continuous since its onset, with hiatuses of only

Li C., Liu Q., Liu L., Li Y., Zhao X., Liu Z.

This study focuses on the simulation of the natural attenuation of groundwater contaminated by acid-leached uranium at a decommissioned uranium mining site. Although natural attenuation by mixing and dilution, pH buffering, adsorption, and reduction has been well described, little research on the simulation of the natural attenuation of groundwater U6+ and sulfuric acid in sandstone aquifers after mining has been performed. Using PHREEQC Version 3 software and the minteq.v4.dat database, in this paper, the thermodynamic adsorption equilibrium constants and adsorption site parameters were modified based on the experimental results of the mineral composition, chemical reactions, U6+ adsorption, and SO42− reduction reactions. This study provides a basis for establishing detailed environmental background data files, conducting laboratory experiments, and predicting the natural attenuation capability of sandstone aquifers at uranium mining sites and their surrounding areas.

Kozakov I.K., Anosova M.O., Kirnozova T.I., Plotkina Y.V., Tolmacheva E.V., Erdenezhargal C.

The crystal complexes of the Hercynian South Altai Metamorphic Belt (SAMP), which is a part of the Central Asian Folded Belt, with a length of more than 1500 km, compose tectonic plates of different scales, in which the level of metamorphism in the early stages reached the conditions of high-temperature subfacies of amphibolite and, in places, granulite facies. In tectonic terms, the band of their exits is confined to the outskirts of the North Asian Caledonian continent, stretching from southeast to northwest along the southern slope of the Gobi, Mongolian and Chinese Altai to Eastern Kazakhstan, where they are represented in the Irtysh shear zone. Poly- and monometamorphic complexes have been established as a part of the SAMP. The age of granitoids of the late episode of metamorphism was determined for the Tsel tectonic plate of the Gobi Altai in the southeastern part of the SAMP: from 374 ± 2 to 360 ± 5 million years. These and previously obtained results show that the early episode of low-pressure metamorphism and the late episode of high-pressure metamorphism occurred in the intervals of ~390–385 and 375–360 MA, respectively, almost throughout this belt. In the interval between them, a short-term stabilization stage is fixed. These processes occurred during the closure of the basin with the oceanic crust of the Tethys series of the South Mongolian Ocean (Paleothesis I). The spatial position of the SAMP is due to the asymmetry of the structure of the basin, in which the active continental margin is represented along its northern part, and the passive one along the southern (in modern coordinates).

Seigneur N., Grozeva N., Purevsan B., Descostes M.

More than 60% of worldwide uranium production is based on the In Situ Recovery mining technique. This exploitation method directly falls within the scope of the applications of reactive transport modelling to optimize uranium production and limit its associated environmental impact. We propose a modelling approach which is able to represent the natural evolution of an aquifer impacted by an ISR test performed using sulfuric acid. The model is calibrated on a 12 year-long data series obtained from 12 monitoring wells surrounding an ISR pilot cell. Through this process-based approach, we simulate the impact of several remediation strategies that can be considered in these contexts. In particular, we model the impact of Pump & Treat combined with reverse osmosis, as well as the circulation of non-impacted fluids through the reservoir with different operating strategies. Our approach allows to compare the effectiveness of these strategies. For this small-scale ISR pilot, monitored natural attenuation constitutes an interesting approach due to its faster pH recovery time with respect to Pump & Treat (5–10 years to pH ∼ 6), whose efficiency can be improved by the addition of exchangeable cations. Circulation of unimpacted fluids can reduce pH recovery times if performed for periods longer than the ISR exploitation and/or deployed with a delay. Combined with an economic evaluation of their deployment, this modelling approach can help the mining operator select and design optimal remediation strategies from an environmental and economical standpoint.

Xu L., Zhang J., Yang Z., Li Q., Cheng Y., Chen S.

Geothermal resources are composed of rock and water, in which water-rock interaction (WRI) has a great influence on the physical properties of thermal reservoirs. The Red River Fault is abundant in different kinds of geothermal resources and the main thermal reservoirs are sandstones and limestones. The study has used the water chemistry, X-ray diffraction (XRD), N2 adsorption, mercury injection, scanning electron microscopy (SEM), physical parameters, and WRI simulation experiments to study the physical properties changes in thermal reservoirs. The pores of thermal reservoirs are mainly intragranular and intergranular pores, in which sandstones are dominated by micropores and mesopores while limestones are dominated by macropores. Through the WRI simulation experiment, the reservoirs have generated many dissolution pores and microfractures, of which the pore-throat connectivity has deteriorated. The changes of physical parameters can be divided into two stages with opposite trends, in which the first stage is controlled by temperature and pressure while the second stage is influenced by dissolution and precipitation. The study has suggested that the change stage of physical properties should be clarified to update the resource quantity dynamically in the development process and the components of fracturing fluids should be studied to achieve the optimal improvement of physical properties and reduce the adverse impact on pore-throat connectivity before the development engineering.

Tugjamba N.

In the first section of the chapter, the overview of Mongolian hydrological research is introduced. The geographical background of the surface water is introduced in the second part, describing the morphological, hydrological and ecological characteristics of rivers and lakes, including the description of the genetic lake types. Detailed analysis is given on the TuulTuul and Ulz River, Lake KhuvsgulKhuvsgul, and ShargaljuutShargaljuut mineral spa. The surface water body, such as rivers, streams and lakes cover 10,560 sq. km or 0.67% of the total territory. Mongolia is divided into three hydrological basins, such as Northern Arctic Ocean BasinArctic Ocean basin, Pacific Ocean BasinPacific Ocean Basin and Central Asian Internal Drainage BasinCentral Asian Internal Drainage Basin, in the Central and Eastern Asia. The total surface water resource of Mongolia is estimated at 599 km3/year. The main water resource is stored in lakes (500 km3/year) and glaciersGlaciers (62.9 km3/year). Water resource in the rivers is shared only 5.8% of the total surface water resources, that is, 34.6 km3/year. The third section introduces groundwaterGroundwater resources and its geographical distributionGeographical distribution. The amount of water resources in the renewable groundwaterGroundwater (i.e., groundwaterGroundwater with a smaller residence time that can be replenished relatively quickly) is estimated at 10.8 km3/year. GroundwaterGroundwater is the main source for drinking, agricultural and industrial usage in Mongolia.

Kaven J.O., Templeton D.C., Bathija A.P.

Geothermal energy is a global renewable resource that has the potential to provide a significant portion of baseload energy in many regions. In the United States, it has the potential to provide 8.5% of the electric generation capacity by the middle of the century. In general, geothermal systems require heat, permeability, and water to be viable for energy generation. However, with current technologies, only heat is strictly necessary in a native system. Engineered geothermal systems (EGS) introduce water into the subsurface at elevated pressures and reduced temperatures and enhance permeability through hydraulic and/or shear fracturing. Additionally, although moderate- to high-temperature resources currently dominate geothermal energy production, low-temperature resources have been utilized for direct-use cases. When well balanced and maintained, geothermal resources can produce significant amounts of heat and achieve long-term sustainability on the order of an estimated tens to hundreds of years.

Zhang B., Zhao D., Zhou P., Qu S., Liao F., Wang G.

Groundwater is undoubtedly important for water supplies and eco-environment protection, especially for arid and semi-arid regions. Analyzing the characteristics and evolution of groundwater is significant for the rational management of groundwater resources. This study investigated the hydrogeochemical characteristics and evolutions of groundwater in the Delingha area, northeast of the Qaidam Basin, northwest China, with a total of 123 water samples, including 105 unconfined groundwater samples, 12 confined groundwater samples, and 6 surface water samples. Hydrochemical results showed that the unconfined and confined groundwater presented diversity in ion concentration. Total Dissolved Solids (TDS) of the unconfined groundwater increased from 146.5 to 8954 mg/L along the groundwater flow direction. The groundwater hydrochemical types were HCO3-Ca·Mg and HCO3·SO4-Ca·Mg in the mountain front area, SO4·HCO3-Ca·Mg and SO4·Cl-Ca·Mg types in the alluvial-lacustrine plain, and Cl·SO4-Na and Cl-Na types in the lacustrine plain. The saturation index showed that parts of the groundwater samples were supersaturated with carbonate minerals (calcite and dolomite); however, all the samples were undersaturated with evaporite minerals (halite and gypsum). Groundwater chemical evolution is mainly controlled by evaporite and carbonate mineral dissolutions, aluminosilicates weathering, and cation exchange.

Fan, Pang, Liao, Tian, Hao, Huang, Li

The Ganzi geothermal field, located in the eastern sector of the Himalayan geothermal belt, is full of high-temperature surface manifestations. However, the geothermal potential has not been assessed so far. The hydrochemical and gas isotopic characteristics have been investigated in this study to determine the geochemical processes involved in the formation of the geothermal water. On the basis of δ18O and δD values, the geothermal waters originate from snow and glacier melt water. The water chemistry type is dominated by HCO3-Na, which is mainly derived from water-CO2-silicate interactions, as also indicated by the 87Sr/86Sr ratios (0.714098–0.716888). Based on Cl-enthalpy mixing model, the chloride concentration of the deep geothermal fluid is 37 mg/L, which is lower than that of the existing magmatic heat source area. The estimated reservoir temperature ranges from 180–210 °C. Carbon isotope data demonstrate that the CO2 mainly originates from marine limestone metamorphism, with a fraction of 74–86%. The helium isotope ratio is 0.17–0.39 Ra, indicating that the He mainly comes from atmospheric and crustal sources, and no more than 5% comes from a mantle source. According to this evidence, we propose that there is no magmatic heat source below the Ganzi geothermal field, making it a distinctive type of high-temperature geothermal system on the Tibetan Plateau.

Broussolle A., Sun M., Schulmann K., Guy A., Aguilar C., Štípská P., Jiang Y., Yu Y., Xiao W.

The general structure of the Chinese Altai has been traditionally regarded as being formed by five tectono-stratigraphic ‘terranes’ bounded by large-scale faults. However, numerous detrital zircon studies of the Paleozoic volcano-sedimentary sequences shown that the variably metamorphosed Cambro-Ordovician sequence, known as the Habahe Group, is present at least in four ‘terranes’. It structurally represents deepest rocks unconformably covered by Devonian and Carboniferous sedimentary and volcanic rocks. Calc-alkaline, mostly Devonian, granitoids that intruded all the terranes revealed their syn-subduction related setting. Geochemistry and isotope features of the syn-subduction granitoids have shown that they originated mainly from the melting of youthful sediments derived from an eroded Ordovician arc further north. In contrast, Permian alkaline granitoids, mostly located in the southern part of the Chinese Altai, reflect a post-subduction intraplate setting. The metamorphic evolution of the metasedimentary sequences shows an early MP-MT Barrovian event, followed by two Buchan events: LP-HT mid-Devonian (ca. 400–380 Ma) and UHT-HT Permian (ca. 300–270 Ma) cycles. The Barrovian metamorphism is linked to the formation of a regional sub-horizontal possibly Early Devonian fabric and the burial of the Cambro-Ordovician sequence. The Middle Devonian Buchan type event is related to intrusions of the syn-subduction granitoids during an extensional setting and followed by Late Devonian-Early Carboniferous NE-SW trending upright folding and crustal scale doming during a general NW-SE shortening, responsible for the exhumation of the hot lower crust. The last Permian deformation formed NW-SE trending upright folds and vertical zones of deformation related to the extrusion of migmatites, anatectic granitoids and granulite rocks, and to the intrusions of gabbros and granites along the southern border of the Chinese Altai. Finally, the Permo-Triassic cooling and thrust systems affected the whole mountain range from ca. 265 to 230 Ma. In conclusion, the Chinese Altai represents different crustal levels of the lower, middle and upper orogenic crust of a single Cambro-Ordovician accretionary wedge, heterogeneously affected by the Devonian polyphase metamorphism and deformation followed by the Permian tectono-thermal reworking event related to the collision with the Junggar arc. It is the interference of Devonian and Permian upright folding events that formed vertical boundaries surrounding the variously exhumed and eroded crustal segments. Consequently, these crustal segments should not be regarded as individual suspect terranes.

Soejono I., Čáp P., Míková J., Janoušek V., Buriánek D., Schulmann K.

Sedimentological and detrital zircon provenance study of the Lower Palaeozoic Zuunnuruu, Tsetseg and Sagsai sedimentary formations was carried out in the eastern part of the Hovd Zone in western Mongolia. Sedimentological analysis has revealed two distinct and consecutive types of sedimentary environments. The Lower Ordovician–earliest Silurian sediments had dominantly volcano-sedimentary character, interpreted as reflecting deposition in a proximal part of a Pacific-type accretionary wedge. The upper, mainly Devonian part of the profile has generally siliciclastic flysch-like nature and indicates platform-type depositional setting related to the syn-extensional thinning of the accretionary wedge-system. Detrital zircon age populations of all the three studied formations uniformly show a dominant Neoproterozoic–Ordovician age group at ca. 560–460 Ma, a broad Neo- to Mesoproterozoic peak at ca. 1050–720 Ma, several minor Meso- to Palaeoproterozoic age clusters at ca. 1.4, 1.9 and 2.4 Ga and ca. 400–360 Ma peaks in the youngest Devonian formation. The early Palaeozoic part of the age spectra is interpreted as detritus mainly derived from the magmatic rocks of the Cambrian–Ordovician Ikh-Mongol Arc System within the nearby Lake Zone and the youngest ages from the neighbouring Devonian granites. The other sources were identified as more distal Tonian magmatic-arc complexes, Rodinia break-up-related volcanic rocks and basement of the Precambrian Zavkhan and Baidrag continental blocks even further east. The maximum sedimentary ages, determined by the youngest detrital zircons, shift the end of deposition of the Sagsai Formation at least to the latest Devonian. Nearly identical detrital zircon age spectra from Lower Palaeozoic sequences of the Hovd Zone and other parts of the Altai belt support an existence of a single giant accretionary complex developed along the entire outer margin of the Ikh-Mongol Arc System. The change in the sedimentary style suggests the latest Ordovician–earliest Silurian termination of magmatic-arc activity in the western Lake Zone, marking the onset of late Silurian–Devonian crustal extensional period in the Altai accretionary system.

Xiao W., Windley B.F., Han C., Liu W., Wan B., Zhang J., Ao S., Zhang Z., Song D.

The architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components, but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined, because of unavailable data. The Central Asian Orogenic Belt (CAOB) provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage. In this paper we review several lines of available evidence, which enable us to propose a new tectonic model of huge roll-back in the formation of the accretionary tectonics of the Mongolian collage in Central Asia. In the early Paleozoic the Mongolia collage comprised the southern Siberian and the Tuva-Mongol Oroclines. The Siberia Craton and the Mongolia collage jointly formed a giant “tadpole-shape” within the Paleo-Asian and Panthanlassic oceans; its head (Siberia) was to the south, and the tail (Tuva-Mongol) to the northwest. The structures and tectonic zonation of the Mongolia collage are characteristic of multiple arcs, which have been separately described in detail in different segments southwards from the Southern Siberia-East Sayan, West Sayan-Gorny Altai-Chara, via the Lake Zone-Junggar-Tianshan, Gobi Altai-Beishan-Alxa, to the Manlay-Hegenshan-Baolidao-Solonker segments. Almost all segments underwent Early Paleozoic to Permian, or even Triassic, frontal subduction and accretion, while rifting in the Late Carboniferous to Permian or Triassic occurred in the outward/oceanward (westward) advancing Mongolian collage. Therefore, we suggest that a huge complex roll-back, active from the Carboniferous to Permian or even to late Triassic, facilitated the formation of the Mongolian collage. The outward multiple roll-back process was compatible and almost coeval with the start of the Tuva-Mongol Orocline and rotation of the Siberian Craton, as confirmed by paleomagnetic and structural data. During the roll-back processes an archipelago paleogeography was formed behind the frontal subduction and accretion, in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times. The roll-back process was affected by the collision of the Kazakhstan collage along the Chara and Karamay zones in the Early Permian, the collision of the Tarim Craton along the South Tianshan zone in the Early Permian, the collision of the Dunhuang Block along the Liuyuan zone in the Early Permian-Triassic, the collision of the Alxa block along the Qugan Qulu zone in the Permian, and the collision of the North China Craton along the Solonker zone in the Middle-Late Triassic. The tectonic styles and architecture of accretionary orogenic belts like the CAOB are characterized both by the amalgamation of multiple terranes and by oroclinal bending. The systematic anatomy of the multiple roll-back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens.

Skuzovatov S.Y., Shatsky V.S., Dril S.I., Perepelov A.B.

We present the detailed mineralogical, geochemical (major and trace element), bulk Nd and Sr and mineral O isotope data for eclogites, associated orthogneisses and metasedimentary rocks from the recently discovered eclogite-bearing complex of the Zamtyn-Nuruu range (SW Mongolia). Trace element studies reveal the enrichment of eclogites with LILE and LREE relative to typical mid-ocean ridge basalts at similar levels of HREE and HFSE but without a clear arc-derived Nb minimum. The eclogites have relatively narrow range of mostly radiogenic eNd(T) values (+2.3 to +3.7 as back-calculated for 550 Ma) and model age TDM of 1.47–1.77 Ga at a wide range of initial 87Sr/86Sr ratio due to variable LILE mobilization in pre- or synmetamorphic processes. The geochemical and isotope data indicate the variably enriched MORB-like protolith for eclogites that have their variable composition through differentiation of precursor melts, slightly enriched mantle source and/or variable degree of crustal contamination. The mostly siliciclastic eclogite-hosting metasediments are likely derived from the intra-continental riftogenic basin, whereas the medium-pressure metapelites of the Maykhan Tsakhir formation originate from deeper passive margin sedimentation. Their Mesoproterozoic two-stage model age TDM−2ST of 1.49–1.63 Ga and crustal eNd(T) values (−3.5 to  −5.3) significantly differ from the Zamtyn Nuruu complex rocks and indicate a mixed Nd source likely resembled from the juvenile Neoproteorozoic magmatism with depleted Nd signatures and the older Meso- or Paleoproterozoic crustal substrate. Contrastingly, eclogite-hosting gneisses exhibit the eNd(T) of the ancient crust (−12.9) and Paleoproterozoic model age TDM−2ST of 2.22 Ga. Both eclogites and metasediments evidently exhibit an input from the ancient crustal source that may be represented by orthogneisses of the Alag Khadny complex. Oxygen isotope data (δ18O of garnets mostly within +5.5 to +6.6) at high Fe3+/ΣFe ratio of bulk rocks (0.15–0.21) indicate variable but mostly limited interaction of precursor rocks with oceanic water, degassing at shallow crustal level or at the surface or relatively more oxidized (back-arc or subarc) mantle source. Considering the limited trace element evidence for the input from continental crust, generally elevated Fe3+/ΣFe for samples showing different retrograde alteration degrees, and no or limited δ18O evidence of pre-metamorphic interaction with oceanic water, we may suggest that primitive low-K tholeitic basalts close to T-MORB tholeites derived from a heterogeneously enriched mantle source of a rifted continental margin as precursor rocks for the studied eclogites. As a consequence of the geological structure and geochemical evidence, connection of rifting to the Rodinia break-up is proposed.

Yousif M., El-Aassar A.H.

The interaction between rocks and groundwater can be considered as multi-faceted processes in hydrogeology where the groundwater chemistry can be resulted from leaching and/or minerals dissolution. The scientific approach of this study based on testing the contribution of remote sensing in providing information related to rock-groundwater interaction along with the outputs of the geochemical model. The current research aims to explore the impacts of lithologic nature and structural geology on the groundwater chemistry. The mentioned objective is significant for the future sustainable development of groundwater in hyper-arid regions. Therefore, both geology and geochemistry of water-bearing formations along the flow path to the studied aquifers were identified. The area was chosen as an example from hyper-arid region to carry out this scientific approach. The obtained results indicate the existence of three main aquifers: Quaternary alluvial (salinity 1253 mg/l to 18,854 mg/l), Nubian Sandstone (salinity 311 mg/l to 14,388 mg/l), and fractured basement (salinity 320 mg/l to 19,375 mg/l). The results of speciation modeling showed that studied aquifers are supersaturated with gibbsite, goethite, hematite, magnetite, aragonite, calcite, dolomite, and alunite. Nubian aquifer specifically has homogeneity results due to the similarity of water-bearing and geology of watersheds (ferruginous sandstone and ironstone). Remote sensing data and digital elevation model analyses were used for generation of the thematic layers which is affecting the groundwater occurrences and quality such as geology, geomorphology, structural lineaments, slope, flow direction, drainage lines, and elevations. The current research concluded that the groundwater chemistry can be a signature of the rock-water interaction. The potential implications of the research are represented through a priority map for groundwater exploration for both hydro-geophysical investigation and testing wells in order to evaluate the groundwater capabilities where the data from the recorded wells were used to calibrate this map.

Nguyen H., Hanžl P., Janoušek V., Schulmann K., Ulrich M., Jiang Y., Lexa O., Altanbaatar B., Deiller P.

Baaran and Baytag “terranes” form important part of the Trans-Altai Zone of the Central Asian Orogenic Belt in the SW Mongolia. The Trans-Altai Zone represents an oceanic domain built by Ordovician to Devonian ophiolites covered by Devonian–Carboniferous oceanic sediments. This oceanic assemblage was intruded by a spectrum of Carboniferous volcanic rocks ranging from basalts to rhyolites (325.6 ± 1.4 Ma to 351.0 ± 5.9 Ma; LA-ICP-MS U–Pb dating on zircon) that display similar whole-rock trace-element and Sr–Nd isotopic signatures regardless their silica contents and the “terrane” they belong to. They are normal-K calc-alkaline rocks whose NMORB-normalized multielement patterns show an arc-like enrichment in LILE (Large Ion Lithophile Elements) and deep negative TNT (Ta, Nb, Ti) anomalies. Based on the relatively high Nb/Yb and Th/Yb ratios, the arc was probably formed on immature continental rather than typical oceanic crust. Low (87Sr/86Sr)i (0.7043–0.7047), high e Nd 350 (+5.2 to = +5.8) and the observed in-situ Hf isotopic variation in dated zircons ( e Hf t  = +7.4 to +13) are all attributed to a partial melting of primitive and youthful (Neoproterozoic–Ordovician) arc-type lower continental crust (metamorphosed intermediate–acid igneous rocks and/or arc-derived greywackes), augmented with, and most likely facilitated by, contemporaneous arc-related basaltic intrusions. A distinct possibility remains the previously formulated model assuming that the Carboniferous magmatism in Gobi-Altai and Trans-Altai zones sampled the juvenile Neoproterozoic to Cambrian arc crust relaminated under the Ordovician–Devonian oceanic crust. In any case, the studied arc association, together with lithological sequence of ophiolites, can be closely correlated with the Dulate arc in eastern Junggar. It is proposed that the two arc sequences form a single belt, c. 500 km long, that represents one of the main known arc structures in the Central Asian Orogenic Belt.

Shestakova A., Guseva N., Kopylova Y., Khvaschevskaya A., Polya D., Tokarev I.

Keith M., Smith D.J., Jenkin G.R., Holwell D.A., Dye M.D.

Pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including Au and Co and the semi-metals As, Se, Sb, Te and Bi. As such, in many hydrothermal ore deposits, where pyrite is the dominant sulphide phase, it can represent a major repository for these elements. Furthermore, the concentrations and ratios of Au, As and Co in pyrite have been used to infer key ore-forming processes. However, the mechanisms controlling the distribution of Te and Se in pyrite are less well understood. Here we compare the Te and Se contents of pyrite from a global dataset of Carlin-type, orogenic Au, and porphyry-epithermal deposits to investigate: (1) the potential of pyrite to be a major repository for these elements; and (2) whether Te and Se provide insights into key ore-forming processes. Pyrite from Carlin-type, low-sulphidation and alkaline igneous rock-hosted epithermal systems is enriched in Te (and Se) compared to pyrite from high-sulphidation epithermal and porphyry Cu deposits. Orogenic Au pyrite is characterised by intermediate Te and Se contents. There is an upper solubility limit for Te as a function of As in pyrite, similar to that established for Au by Reich et al. (2005) ; and this can be used to identify Te present as telluride inclusions, which are common in some epithermal-porphyry and orogenic Au deposits. Physicochemical fluid parameters, such as pH, redox and temperature, as well as crystal-chemistry control the incorporation and concentration of Se and Te in pyrite. Neutral to alkaline fluids have the ability to effectively mobilise and transport Te. Fluid boiling in porphyry-epithermal systems, as well as wall rock sulphidation and oxidation in Carlin-type (and orogenic Au) deposits can effectively precipitate Te in association with pyrite and Au. In contrast, Se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature, irrespective of pH and f O 2 . Hence, we propose that the Se contents of pyrite may be used as a new geo-thermometer for hydrothermal ore deposits. Furthermore, the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for Te and Se in Carlin-type and some epithermal systems, and thus pyrite can be considered to be of economic interest as a potential source for these elements.

Lund J.W.

Besser H., Mokadem N., Redhaounia B., Hadji R., Hamad A., Hamed Y.

In southern Tunisia, the lack of permanent surface water, associated with drought conditions, leads to an endless abstraction from the limited low renewable multi-layered aquifer system of Système Aquifère du Sahara Septentrional containing two principal aquifers, the complex terminal and the Continental Intercalaire (CI) multi-layered systems. The deepest aquifer embodies the low-enthalpy thermal resources of Southern Tunisia. The thermo-mineral surface manifestations of the conductively heated waters reveal the complexity of the geotectonic history of the region and create oases systems in net contrast to the desertic landscape of the Chotts region. As agriculture constitutes the principal economic activity in the studied area and as it is currently threatened by thermal water quality degradation, the present hydrogeological investigation aims for a characterization of the CI thermal resources on the basis of a critical quality evaluation. Thus, different geothermometry approaches have been applied to characterize the low-enthalpy thermal field showing a temperature ranging from 27 to 72 °C. The application of cations geothermometers owns to different temperature estimations ranging from 28 to 202 °C. Based on Na+–Mg2+–K+, K+–Mg2+–Ca2+ and HCO3−–Cl−–SO42− geoindicators, the CI thermal resources refer to immature waters characterized by MI varying from − 0.5 to 0.19. The assessment of groundwater chemical composition based on a Durov diagram proves that CI thermal water is governed by mixing between different water bodies with relative abundance of Na+, Cl−, and SO42− elements. According to D’Amore genetic diagram and meteoric genesis indices, the analyzed groundwater derived from deep circulation in sandy formations. The water quality can change along fluid migration pathways expressed by scattered isotopic and chemical data and a number of mixing ratios. Most changes in the background CI composition result from continuous pumping that modifies natural flows and increase quality degradation.

Janoušek V., Jiang Y., Buriánek D., Schulmann K., Hanžl P., Soejono I., Kröner A., Altanbaatar B., Erban V., Lexa O., Ganchuluun T., Košler J.

The Khantaishir Magmatic Complex (KMC) (south–central Mongolia) exposes a section of a magmatic system consisting of deep crustal, ultramafic cumulates (coarse-grained Amp gabbros and hornblendites; c. 0.35–0.5 GPa) to shallower crustal levels dominated by Amp–Bt tonalites ( c. 0.1–0.2 GPa). The magmatic rocks were emplaced during most of the Cambrian ( c. 538–495 Ma) and are mostly geochemically primitive (Mg# ~ 50), Na-rich and metaluminous. The (normal-) calc-alkaline signature and characteristic trace-element enrichment in hydrous-fluid mobile large-ion lithophile elements (LILE) relative to high-field strength elements (HFSE) suggest an origin within a magmatic arc. Multiple intrusions of basic magma derived from a subduction-modified depleted mantle developed by fractional crystallization and/or accumulation of (Ol, Cpx) Amp + Bt, later joined by Pl. Magma mixing with, or without, exchange of xenocrysts between compositionally dissimilar melt batches was also important. Over time, partial melting of older, lower crustal metabasic rocks became increasingly significant, again with a strong subduction signature. The lack of zircon inheritance in the magmatic products and rather high zircon e Hf t values (all >+3, but for most samples > +8) as well as whole-rock Sr–Nd isotopic compositions imply that the arc was not founded on mature continental crust. It was probably located at the margin of the Baydrag microcontinent, dominated by accreted metabasic rocks of an older (early Tonian?) island arc covered by a thin layer of subordinate metasediments containing detrital zircons with Tonian and ill-defined Palaeoproterozoic ages. The KMC represents a small vestige of an extensive Cambrian–Ordovician subduction system (termed here the Ikh-Mongol Arc System), bordering the western margin of a chain of Precambrian microcontinents (Tuva-Mongolia, Zabkhan and Baydrag) that, together with accreted Neoproterozoic marginal basins (the Lake Zone), defines the external part of the Mongolian orocline.