Sorption/desorption kinetics for selected radionuclides (99Tc(VII), 232Th(IV), 233U(VI), 237Np(V), 242Pu and 243Am(III)) under Grimsel (Switzerland) ground water conditions (pH 9.7 and ionic strength of ∼1 mM) in the presence of synthetic Zn or Ni containing montmorillonite nanoparticles and granodiorite fracture filling material (FFM) from Grimsel were examined in batch studies. The structurally bound Zn or Ni in the octahedral sheet of the synthetic colloids rendered them suitable as colloid markers. Only a weak interaction of the montmorillonite colloids with the fracture filling material occurs over the experimental duration of 10,000 h (∼13 months). The tri- and tetravalent radionuclides are initially strongly associated with nanoparticles in contrast to 99Tc(VII), 233U(VI) and 237Np(V) which showed no sorption to the montmorillonite colloids. Radionuclide desorption of the nanoparticles followed by sorption to the fracture filling material is observed for 232Th(IV), 242Pu and 243Am(III). Based on the conceptual model that the driving force for the kinetically controlled radionuclide desorption from nanoparticles and subsequent association to the FFM is the excess in surface area offered by the FFM, the observed desorption kinetics are related to the colloid/FFM surface area ratio. The observed decrease in concentration of the redox sensitive elements 99Tc(VII), 233U(VI) and 237Np(V) may be explained by reduction to lower oxidation states in line with Eh-pH conditions prevailing in the experiments and thermodynamic considerations leading to (i) precipitation of a sparingly soluble phase, (ii) sorption to the fracture filling material, (iii) possible formation of eigencolloids and/or (iv) sorption to the montmorillonite colloids. Subsequent to the sorption/desorption kinetics study, an additional experiment was conducted investigating the potential remobilization of radionuclides/colloids attached to the FFM used in the sorption/desorption kinetic experiments by contacting this FFM with pure Grimsel groundwater for 7 days. A positive correlation of 242Pu, 232Th(IV) and 237Np was observed with the Zn and Ni concentrations in the desorption experiments indicating a remobilization of sorbed montmorillonite colloids. The results of the study in hand highlight (i) the novel use of structural labeled colloids to decrease the uncertainties in the determination of nanoparticle attachment providing more confidence in the derived radionuclide desorption rates. Moreover, the data illustrate (ii) the importance of radionuclide colloid desorption to be considered in the analysis and application of colloid facilitated transport both in laboratory or in-situ experiments and numerical model simulations and (iii) a possible remobilization of sorbed colloids and associated radionuclides by desorption from the matrix material (FFM) under non-equilibrium conditions.
In Peru, energy production is more than 75 % dominated by hydrocarbons (IEA, 2018) while at the same time, the Andes forearc is in a full demographic and economic development. However, the geothermal potential associated with reverse fault in the mountain range forearcs remains poorly studied compared to normal faults.  It is then essential to evaluate the geothermal potential associated with the Andes forearc thrust faults, in considering the environmental risks associated.The hydrothermal system associated with the Sama-Calientes fault, near the city of Tacna South of Peru (18°S) is a suitable field site to experiment how integrated studies could provide an exploration diagnostic. The Calientes hot springs (42-44°C) emerge on the Sama-Calientes fault, an active thrust which delimits the border between the Andes and the north extension of the Atacama Desert. With an integrated study of the hydrothermal fluids and gas geochemistry, XRD composition of the hydrothermal deposits and veins, structural geology, and 3D numerical modeling with COMSOL Multiphysics, we propose to characterize the thermal anomaly associated with the Calientes springs and faults, putting them in perspective with the other hydrothermal springs in the region. Preliminary results indicated that hydraulic breccia, veins, and concretions around the Calientes springs and faults are mainly composed of calcite, contrarily to the other hot springs sites inside the Andes (excepted the Ticaco hot springs). Free and dissolved gas of the springs associated with the high Andean volcanoes (Casiri, Yucamani, Tacora) are mainly composed of CO2 (90-100%), while those associated with the pre-andean faults (Sama-Calientes, Incapuquio) are mainly composed of N2 (60-100%). Volcanic-associated springs show high sulfate concentrations (48-54 mmol/L) compared to fault-associated springs (3-25 mmol/L).  A simple 3D numerical model with a surface DEM and a homogenous permeability indicates that the topography-driven flow lines contributing to the Calientes springs would come from the Tacora volcano, 40 km north-east of Calientes. More investigation will precise the organization of the hydrothermal cells and the associated thermal anomalies. This work will also contribute to understand the role of hydrothermal fluids in subduction zones and especially on seismogenic reverse fault dynamics.
This study provides a comprehensive characterization of various hydrothermal sys- tems in Southern Peru ranging from the faulted Precordillera’s steep topography up to the volcanic High Cordillera (>4000 m asl). The objective is to investigate thermal anoma- lies that may potentially serve as new geothermal resources.Our integrated approach com- bines: i) geochemistry from 14 hot springs sampled throughout the Tacna region, and ii) 3D numerical modeling of coupled groundwater and heat transfer considering topog- raphy and faults embedded in homogeneous permeability. Water and gas analysis indi- cates that the springs located near volcanoes discharge Na-K-Cl waters with high tem- peratures (>87°C), high Total Dissolved Solid concentrations (TDS >3452 mg/L), and free gases dominated by CO2 (>90 vol%). Springs located along the regional faults in the Precordillera discharge Ca-SO4 and Na-K-Cl waters with moderate temperatures (27- 53°C), intermediate TDS concentrations (464-2458 mg/L), radiocarbon ages between 1.4 and 7.9 kyr, and free gases dominated by N2 (>95 vol%). The Aruma springs, which are located at the transition between the High and the Precordillera, display intermediate characteristics. Numerical models accurately replicate the locations and temperatures of the fault-related springs only for permeable faults (>10 m), revealing the creation of 100-km long thermal plumes along faults, locally rising up the 150°C-isotherm to about ∼ 1000 m below the surface. This approach clearly distinguishes the spring origins, which are volcanic in High Cordillera and tectonic in Precordillera. Moreover, we highlight that steep topographic gradient and permeable reverse faults in the Andean forearc may gen- erate considerable thermal anomalies, opening perspectives for the geothermal exploration.
Abstract The main event responsible for the deposition of tungsten at Panasqueira was closely associated with strong tourmalinization of the wall rocks. Tourmaline is coeval with a W-rich rutile (up to 8–10 wt % W), and both minerals record an early introduction of W in the system, just before the main W deposition. Uranium-Pb dating of the rutile by LA-ICP-MS yielded an age of 305.2 ± 5.7 Ma, which is 6 to 10 m.y. older than the K-Ar age of 296.3 ± 1.2 Ma obtained on muscovite, which was therefore not coeval with wolframite. Major and trace element concentration variations in tourmaline record fluid mixing between two end members, both considered to be of metamorphic derivation on the basis of rare earth element profiles. We report evidence for a fluid rich in Co, Cu, Pb, Sc, Sr, V, Cr, Nb, Ta, and Sn interpreted to be of local origin—e.g., well equilibrated with the host formations—and a fluid rich in Li, F, Fe, Mn, and W inferred to be of deep origin and related to biotite dehydration. The second fluid carried the metals (in particular Fe and Mn) that were necessary for wolframite deposition and that were not necessarily inherited from the wall rocks through fluid-rock interaction. Micrometer-scale variations in tourmaline and rutile crystal chemistry are indicative of pulsatory fluid input during tourmalinization.
