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

The near-surface water cycle in a geologically complex area comprises very different sources including meteoric, metamorphic and magmatic ones. Fluids from these sources can react with sedimentary, magmatic and/or metamorphic rocks at various depths. The current study reports a large number of major, minor and trace element analyses of meteoric, mineral, thermal and mine waters from a geologically well-known and variable area of about 200 × 150 km in SW Germany. The geology of this area comprises a Variscan granitic and gneissic basement overlain in parts by Triassic and Jurassic shales, sandstones and limestones. In both the basement and the sedimentary rocks, hydrothermal mineralization occurs (including Pb, Cu, As, Zn, U, Co and many others) which were mined in former times. Mineral waters, thermal waters and meteoric waters flowing through abandoned mines (mine waters) are distributed throughout the area, although the mine waters concentrate in and around the Schwarzwald.The present analyses show, that the major element composition of a particular water is determined by the type of surrounding rock (e.g., crystalline or sedimentary rocks) and the depth from which the water originates. For waters from crystalline rocks it is the origin of the water that determines whether the sample is Na–Cl dominant (deeper origin) or Ca–HCO₃ dominant (shallow origin). In contrast, compositions of waters from sedimentary rocks are determined by the availability of easily soluble minerals like calcite (Ca–HCO₃ dominant), halite (Na–Cl dominant) or gypsum (Ca–SO₄ dominant). Major element data alone cannot, therefore, be used to trace the origin of a water. However, the combination of major element composition with trace element data can provide further information with respect to flow paths and fluid–rock interaction processes. Accordingly, trace element analyses showed, that:

• −Ce anomalies can be used as an indicator for the origin of a water. Whereas surface waters have negative or strongly negative Ce anomalies, waters originating from greater depths show no or only weak negative Ce anomalies.
• −Eu anomalies can be used to differentiate between host rocks. Waters from gneisses display positive Eu anomalies, whereas waters from granites have negative ones. Waters from sedimentary rocks do not display any Eu anomalies.
• −Rb and Cs can also be indicators for the rock with which the fluid interacted: Rb and Cs correlate positively in most waters with Rb/Cs ratios of ∼2, which suggests that these waters are in equilibrium with the clay minerals in the rocks. Rb/Cs ratios >5 indicate reaction of a water with existing clay minerals, whereas Rb/Cs ratios <2 are probably related to host rock alteration and clay mineral formation.

The chemical compositions of carbonate precipitates from thermal waters indicate that rare earth elements (REEs), Rb and Cs concentrations in the minerals are controlled by the incorporation of clay particles that adsorb these elements.     

Be-daughter minerals in fluid and melt inclusions: implications for the enrichment of Be in granite–pegmatite systems

The study of re-homogenized melt inclusions in the same growth planes of quartz of pegmatites genetically linked to the Variscan granite of the Ehrenfriedersdorf complex, Erzgebirge, Germany, by ion microprobe analyses has determined high concentrations of Be, up to 10,000 ppm, in one type of melt inclusion, as well as moderate concentrations in the 100 ppm range in a second type of melt inclusion. Generally, the high Be concentrations are associated with the H₂O- and other volatile-rich type-B melt inclusions, and the lower Be concentration levels are connected to H₂O-poor type-A melt inclusions. Both inclusion types, representing conjugate melt pairs, are formed by a liquid–liquid immiscibility separation process. This extremely strong and very systematic scattering in Be provides insights into the origin of Be concentration and transport mechanisms in pegmatite-forming melts. In this contribution, we present more than 250 new analytical data and show with ion microprobe and fs-LA-ICPMS studies on quenched glasses, as well as with confocal Raman spectroscopy of daughter minerals in unheated melt inclusions, that the concentrations of Be may achieve such extreme levels during melt–melt immiscibility of H₂O-, B-, F-, P-, ± Li-enriched pegmatite-forming magmas. Starting from host granite with about 10 ppm Be, melt inclusions with 10,000 ppm Be correspond to enrichment by a factor of over 1,000. This strong enrichment of Be is the result of processes of fractional crystallization and further enrichment in melt patches of pegmatite bodies due to melt–melt immiscibility at fluid saturation. We also draw additional conclusions regarding the speciation of Be in pegmatite-forming melt systems from investigation of the Be-bearing daughter mineral phases in the most H₂O-rich melt inclusions. In the case of evolved volatile and H₂O-rich pegmatite systems, B, P, and carbonates are important for the enrichment and formation of stable Be complexes.     

LA-ICP-MS mineral chemistry of titanite and the geological implications for exploration of porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt,SW China

The Jinshajiang–Red River alkaline igneous belt in the eastern Indian–Asian collision zone, of southwestern China, hosts abundant, economically important Cu–Mo–Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe₂O₃/Al₂O₃, ΣREE?+?Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al₂O₃, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE?+?Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO₂ conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt, and to other areas.     

Thermal properties of harzburgite and dunite at 0.8–3 GPa and 300–823 K and implications for the thermal evolution of Tibet

Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus.The results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing pressure.By combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic ages.The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.     

Microtextural and mineral chemical analyses of andesite–dacite from Barren and Narcondam islands: Evidences for magma mixing and petrological implications

Andesite and dacite from Barren and Narcondam volcanic islands of Andaman subduction zone are composed of plagioclase, orthopyroxene, clinopyroxene, olivine, titanomagnetite, magnesio-hornblende and rare quartz grains. In this study, we use the results of mineral chemical analyses of the calc-alkaline rock suite of rocks as proxies for magma mixing and mingling processes. Plagioclase, the most dominant mineral, shows zoning which includes oscillatory, patchy, multiple and repetitive zonation and ‘fritted’ or ‘sieve’ textures. Zoning patterns in plagioclase phenocrysts and abrupt fluctuations in An content record different melt conditions in a dynamic magma chamber. ‘Fritted’ zones (An₅₅) are frequently overgrown by thin calcic (An₇₂) plagioclase rims over well-developed dissolution surfaces. These features have probably resulted from mixing of a more silicic magma with the host andesite. Olivine and orthopyroxene with reaction and overgrowth rims (corona) suggest magma mixing processes. We conclude that hybrid magma formed from the mixing of mafic and felsic magma by two-stage processes – initial intrusion of hotter mafic melt (andesitic) followed by cooler acidic melt at later stage.     

Stratigraphic and regional distribution of fractures in Barremian–Aptian carbonate rocks of Eastern Oman: outcrop data and their extrapolation to Interior Oman hydrocarbon reservoirs

The carbonates of the Barremian to Aptian Qishn Formation are outcrop equivalents to major hydrocarbon reservoirs in the Middle East and in Oman specifically. The rocks are exposed in the Haushi–Huqf area of eastern Oman where they are affected by pervasive jointing and localized folding and faulting. Information gathered in the Huqf outcrops can be used to formulate predictions on fracture patterns in adjacent reservoirs. Systematic joints are confined to few meters-thick intervals of widely differing lithologies, which can be correlated over hundreds of square kilometers. Over the entire area, systematic joints are typically more than tens of meters long, have spacings of 4–18 cm and homogeneous morphologies. These joints are interpreted to be of Late Aptian age. The dominant set of joints strikes consistently NW–SE and developed parallel to the causative maximum horizontal compression S_H. The direction of compression is at an high angle to the two major tectonic domains of the region, the subsiding Oman Interior basins and the elevated Haushi-Huqf High. NW–SE compression is proposed to have caused crustal/lithospheric buckling and thereby to have controlled Jurassic to Early Tertiary patterns of vertical movements. In such a scenario, the direction of compression is predicted to be constant over the entire domain. It is thus expected that Qishn carbonates in the subsiding Oman Interior basins also experienced NW–SE compression and developed systematic joints similar to those observed in the Huqf region. In the Neogene, with the establishment of the Zagros stress field, the maximum horizontal compression became roughly N–S, thereby possibly leading to the closure of pre-existing joint systems.     

Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems – 2: New experiments with supercritical CO2 and implications for carbon sequestration

In order to evaluate the extent of CO₂–water–rock interactions in geological formations for C sequestration, three batch experiments were conducted on alkali feldspars–CO₂–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis batch systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔG_r relationship can overestimate the extent of feldspar dissolution during CO₂ storage. Finally, the literature on feldspar dissolution in CO₂-charged systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral information at CO₂ storage conditions.     

Retention of Sm–Nd isotopic ages in garnets subjected to high-grade thermal reworking: implications for diffusion rates of major and rare earth elements and the Sm–Nd closure temperature in garnet

Garnet is a vital mineral for determining constrained P–T–t paths as it can give both the P–T and t information directly. However, estimates of the closure temperature of the Sm–Nd system in garnet vary considerably leading to significant uncertainties in the timing of peak conditions. In this study, five igneous garnets from an early Proterozoic 2414 ± 6 Ma garnet—cordierite bearing s-type granite—which was subjected to high-T reworking have been dated to examine their diffusional behaviour in the Sm–Nd system. Garnets 8, 7, 6 and 2.5 mm in diameter were compositionally profiled and then dated, producing two-point Sm–Nd isochron ages of 2412 ± 10, 2377 ± 5, 2370 ± 5 and 2365 ± 8 and 2313 ± 11 Ma, respectively. A direct correlation exists between grain size and amount of resetting highlighting the effect of grain size on closure temperature. Major element EMPA and LA-ICPMS REE traverses reveal homogenous major element profiles and relict igneous REE profiles. The retention of REE zoning and homogenisation of major element zoning suggest that diffusion rates of REEs are considerably slower than that of the major cations. The retention of REE zoning and the lack of resetting in the largest grains suggest that Sm–Nd closure temperature in garnet is a function of grain size, thermal history and REE zoning in garnet.     

SHRIMP U–Pb and Ar–Ar geochronology of major porphyry and skarn Cu deposits in the Balkhash Metallogenic Belt,Central Asia,and geological implications

The Balkhash Metallogenic Belt (BMB) in Kazakhstan, Central Asia, with the occurrence of the super-large Kounrad and Aktogai, the large Borly porphyry Cu–Mo deposits, and the large Sayak skarn polymetallic ore-field, is one of the central regions of the Paleozoic Central Asian metallogenic domain and orogenic belt. In this study, newly obtained SHRIMP zircon U–Pb ages of nine samples and ⁴⁰Ar/³⁹Ar ages of six mineral samples (inclding hornblende, biotite and K-feldspar) give more detailed constraints on the timing of the granitic intrusions and their metallogeny. Porphyritic monzonite granite and tonalite porphyry from the Kounrad deposit yield U–Pb zircon SHRIMP ages of 327.3 ± 2.1 Ma and 308.7 ± 2.2 Ma, respectively. Quartz diorite and porphyritic granodiorite from the Aktogai deposit yield U–Pb SHRIMP ages of 335.7 ± 1.3 Ma and 327.5 ± 1.9 Ma, respectively. Porphyritic granodiorite and granodiorite from the Borly deposit yield U–Pb SHRIMP ages of 316.3 ± 0.8 Ma and 305 ± 3 Ma, respectively. Diorite, granodiorite, and monzonite from the Sayak ore-field yield U–Pb SHRIMP ages of 335 ± 2 Ma, 308 ± 10 Ma, and 297 ± 3 Ma, respectively. Hornblende, biotite, and K-feldspar from the Aktogai deposit yield ⁴⁰Ar/³⁹Ar cooling ages of 310.6 Ma, 271.5 Ma, and 274.9 Ma, respectively. Hornblende, biotite, and K-feldspar from the Sayak ore-field yield ⁴⁰Ar/³⁹Ar cooling ages of 287.3 ± 2.8 Ma, 307.9 ± 1.8 Ma, and 249.8 ± 1.6 Ma, respectively. The new ages constrain the timing of Late Paleozoic felsic magmatism to ∼336 to ∼297 Ma. Skarn mineralization in the Sayak ore-field formed at ∼335 and ∼308 Ma. Porphyry Cu–Mo mineralization in the Kounrad deposit and the Aktogai deposit formed at ∼327 Ma, and in the Borly deposit at ∼316 Ma. The Late Paleozoic regional cooling in the temperature range of ∼600 °C to ∼150 °C occurred from ∼307 to ∼257 Ma.     

Crystal chemistry, thermal expansion, and Raman spectra of hydroxyl-clinohumite: implications for water in Earth’s interior

Two samples of hydroxyl-clinohumite, sample SZ0407B with approximate composition Mg_8.674(14)Fe_0.374(4)(Si_0.99(1)O₄)₄(OH)₂ and sample SZ0411B with composition Mg₉(SiO₄)₄(OH)₂, were synthesized at 12 GPa and 1,250 °C coexisting with olivine. Unit-cell parameters determined by single-crystal X-ray diffraction are given as follows: a = 4.7525(4) Å, b = 10.2935(12) Å, c = 13.7077(10) Å, α = 100.645(9)°, V = 659.04(9) Å³ for SZ0407B, and a = 4.7518(6) Å, b = 10.2861(12) Å, c = 13.7008(9) Å, α = 100.638(9)°, V = 658.15(9) Å³ for SZ0411B. Single-crystal X-ray intensity data were collected for crystal structure refinements of both samples. Relative to the pure-Mg sample, Fe decreases M3–OH bond lengths by ~0.010(3) Å, consistent with some ferric iron ordering into M3. Raman spectroscopy shows two strong bands in the lattice-mode region at 650 and 690 cm^?1 in the Fe-bearing sample, which are not observed in the pure-Mg sample. Spectra in the H₂O region show at least five bands, which are deconvolved into seven distinct O–H-stretching modes. Thermal expansion measurements were carried out for both samples from 153 to 787 K by single-crystal X-ray diffraction. The average a-, b-, c-axial and volumetric thermal expansion coefficients (10^?6 K^?1) are 10.5(1), 12.3(2), 12.5(2) and 34.9(5) for SZ0407B, respectively, and 11.1(1), 12.6(3), 13.7(3), 36.8(6) for SZ0411B, respectively. After heating, the unit-cell parameters were refined again for each sample at ambient condition, and no significant changes were observed, indicating no significant oxidation or dehydration during the experiment. For the DHMS phases along the brucite–forsterite join, linear regression gives a systematic linear decrease in expansivity with increasing density. Further, substitution of ferrous iron into these structures decreases thermal expansivity, making the Fe-bearing varieties slightly stiffer.     

Helium and argon isotopic compositions of the Longquanzhan gold deposit in the Yishu fault zone and their geological implications

The Longquanzhan gold deposit hosted in granitic cataclasites with mylontization of the foot wall of the main Yishui-Tangtou fault. 3He/4He ratios in fluid inclusions range from 0. 14 to 0. 24 R/Ra,close to those of the crust-source helium. 40Ar/36Ar ratios were measured to be 289-1811, slightly higher than those of atmospheric argon. The results of analysis of helium and argon isotopes suggested that ore-forming fluids were derived chiefly from the crust. The δ18O values of fluid inclusions from vein quartz range from -1.78‰ to 4.07‰, and the δD values of the fluid inclusions vary between -74‰ and -77‰. The hydrogen and oxygen isotope data indicated that the ore-forming fluid for the Longquanzhan gold deposit had mixed with meteoric water in the process of mineralization. This is consistent with the conclusion from the helium and argon isotope data.     

Coupled thermal–hydraulic modeling of artificial ground freezing with uncertainties in pipe inclination and thermal conductivity

Acta Geotechnica - Artificial ground freezing (AGF) has been widely used as a temporary soil stabilization and waterproofing technique in geotechnical practices (e.g., tunnel construction). Many...     

Molybdenite Re–Os and albite 40Ar/39Ar dating of Cu–Au–Mo and magnetite porphyry systems in the Yangtze River valley and metallogenic implications

The area of the Middle–Lower Yangtze River valley, Eastern China, extending from Wuhan (Hubei province) to western Zhenjiang (Jiangsu province), hosts an important belt of Cu–Au–Mo and Fe deposits. There are two styles of mineralization, i.e., skarn/porphyry/stratabound Cu–Au–Mo–(Fe) deposits and magnetite porphyry deposits in several NNE-trending Cretaceous fault-bound volcanic basins. The origin of both deposit systems is much debated. We dated 11 molybdenite samples from five skarn/porphyry Cu–Au–Mo deposits and 5 molybdenite samples from the Datuanshan stratabound Cu–Au–Mo deposit by ICP-MS Re–Os isotope analysis. Nine samples from the same set were additionally analyzed by NTIMS on Re–Os. Results from the two methods are almost identical. The Re–Os model ages of 16 molybdenite samples range from 134.7 ± 2.3 to 143.7 ± 1.6 Ma (2σ). The model ages of the five samples from the Datuanshan stratabound deposit vary from 138.0 ± 3.2 to 140.8 ± 2.0 Ma, with a mean of 139.3 ± 2.6 Ma; their isochron age is 139.1 ± 2.7 Ma with an initial Os ratio of 0.7 ± 8.1 (MSWD = 0.29). These data indicate that the porphyry/skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system. Albite ⁴⁰Ar/³⁹Ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 Ma, i.e., 10–20 Ma later. Both mineralization styles characterize transitional geodynamic regimes, i.e., the period around 140 Ma when the main NS-trending compressional regime changed to an EW-trending lithospheric extensional regime, and the period of 125–115 Ma of dramatic EW-trending lithospheric extension.     

Impact of tunneling on regional groundwater flow and implications for swelling of clay–sulfate rocks

Tunnels play a key role in many transportation concepts. The swelling of clay–sulfate rocks leads to serious damage to many tunnels crossing such rock, producing great difficulties and high extra costs in tunnel engineering. The swelling is caused by the transformation of the sulfate mineral anhydrite into gypsum, entailing a 60% volume increase. The transformation involves anhydrite dissolution in water, transport of the solution with groundwater flow, and gypsum precipitation at a different location. Therefore, the knowledge of groundwater flow systems at the tunnel and adjacent areas is essential to better understand the swelling processes. The present study investigates the groundwater flow systems at the Chienberg tunnel in Switzerland before and after the tunnel excavation, based on numerical flow modeling. The models include faults and the hydrostratigraphic layering in the subsurface to assess the role of the hydrogeological setting. The results of this study indicate effects on groundwater flow caused by the tunneling, which may trigger rock swelling by favoring anhydrite dissolution and gypsum precipitation, including (1) increase of flow rates around the tunnel, (2) broadened, shifted and more distributed capture zones leading to a change in origin and age of groundwater, (3) access of groundwater from preferential flow paths (e.g. faults) due to the drainage effect of the tunnel, and (4) change in geochemical equilibrium conditions because of decreased pore water pressures in the tunnel area.     

Tectonic position,geological manifestations of sources,and aftershock processes for a series of strong earthquakes of 2016–2017 in central Italy

Based on seismological, geodynamic, and seismotectonic data on a series of strong earthquakes which occurred in 2016–2017 in central Italy, the tectonic positions and geological manifestations of these events are determined. The aftershock processes of these earthquakes are studied. It is found that epicentral clouds of mainshocks and aftershocks almost overlapped each other, so these earthquake sources in aggregate can be classified as a high-magnitude earthquake swarm.     

Thermodynamic modelling of a cooling C–O–H fluid–graphite system: implications for hydrothermal graphite precipitation

Carbon-saturated crustal fluids in the C–O–H system comprise H₂O, CO₂ and CH₄ as the most important fluid species. Graphite precipitation from a cooling C–O–H is discussed for two different systems, namely for a fluid–rock system in which no transfer of atomic oxygen and hydrogen between the fluid and the rock is possible (closed fluid system), and for an open fluid system. Thermodynamic model calculations show that the graphite-forming reactions and the graphite precipitation potential are different for these two systems. Furthermore, the calculations demonstrate that for both systems, the following factors play a role in determining the graphite precipitation potential, i.e. (1) the redox state of the fluid, (2) the initial pressure and temperature conditions and (3) whether cooling is combined with decompression. Open and closed fluid system graphite precipitation can be distinguished from each other using fluid inclusion and stable carbon isotope studies. The results of this study provide insight in the formation of hydrothermal graphite deposits.