How well suited are current thermodynamic models to predict or interpret the composition of (Ba,Sr)SO₄ solid-solutions in geothermal scalings?

In this study, we report results of the analysis of a particularly interesting scaling sample from the geothermal plant in Neustadt-Glewe in northern Germany, which contained 19% Galena (PbS) and 81% of a heterogeneous assemblage of (Ba,Sr)SO₄ crystals with varying compositions, 0.15 < X$_{Ba}$ < 0.53. A main fraction of the sample (~56%) has a barite content of X$_{Ba}$ ≈ 0.32. We try to relate the solid composition of the (Ba,Sr)SO₄ solid-solution to the conditions at the geothermal plant concerning temperature, pressure, and solution composition, and discuss it with respect to the challenges in modelling the composition of (Ba,Sr)SO₄ solid-solutions on the basis of thermodynamic mixing models. We note that considerable uncertainties are related to the description of (Ba,Sr)SO₄ formation by means of thermodynamic models. The scaling composition observed in this study would be in line with endmember solubilities as predicted by the PhreeqC-Pitzer database for 70 °C and an interaction parameter, a0 = 1.6. According to such a model, the scaling heterogeneity would reflect bimodal precipitation behaviour due to various degrees of depletion of the brine with respect to X(Ba)($_{aq}$). Minor fluctuations in X(Ba)($_{aq}$): 0.0017 < X(Ba)($_{aq}$) < 0.0042 explain the full range of observed solid compositions. The choice especially of the interaction parameter seems to some extent arbitrary. This knowledge gap strongly limits the interpretation of (Ba,Sr) SO₄ compositions. Thus, it is not possible to distinguish between kinetic and thermodynamic effects on partitioning or to use the solid-solution composition to draw conclusions about the precipitation conditions (e.g. Temperature)

The resonance triplet at E_alpha = 4.5 MeV in the 40Ca(alpha,gamma)44Ti reaction

The 40Ca(alpha,gamma)44Ti reaction is believed to be the main production channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation from decaying 44Ti has been observed so far for two supernova remnants, and a precise knowledge of the 44Ti production rate may help improve supernova models. The 40Ca(alpha,gamma)44Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at E_alpha = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the gamma counting, and by in-beam gamma spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to omega gamma = (0.92+-0.20), (6.2+-0.5), and (1.32+-0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5 GK.Comment: 12 pages, 11 figures; submitted to Phys. Rev.

The old, unique C1 chondrite Flensburg - Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies

On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of ~5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of <2 g/cm^3, and a magnetic susceptibility of logX = 4.35 (X in 10^-9 m^3/kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (~3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. 53^Mn-^53Cr ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities occurred no later than 4564.6 +- 1.0 Ma (using the angrite D'Orbigny as the Mn-Cr age anchor). This corresponds to 2.6 +- 1.0 or 3.4 +- 1.0 Ma after formation of CAIs, depending on the exact absolute age of CAIs. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to decay of 26Al. In the three oxygen isotope diagram, Flensburg plots at the 16O-rich end of the CM chondrite field and in the transition field to CV-CK-CR chondrites. The mass-dependent Te isotopic composition of Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, 50Ti and 54Cr isotope anomalies indicate that Flensburg is similar to CM chondrites, as do the ~10 wt.% H2O of the bulk material. Yet, the bulk Zn, Cu, and Pb concentrations are about 30% lower than those of mean CM chondrites. The He, Ne, and Ar isotopes of Flensburg show no solar wind contribution; its trapped noble gas signature is similar to that of CMs with a slightly lower concentration of 20Netr. Based on the bulk H, C, and N elemental abundances and isotopic compositions, Flensburg is unique among chondrites, because it has the lightest bulk H and N isotopic compositions of any type 1 or 2 chondrite investigated so far. Moreover, the number of soluble organic compounds in Flensburg is even lower than that of the brecciated CI chondrite Orgueil. The extraordinary significance of Flensburg is evident from the observation that it represents the oldest chondrite sample in which the contemporaneous episodes of aqueous alteration and brecciation have been preserved. The characterization of a large variety of carbonaceous chondrites with different alteration histories is important for interpreting returned samples from the OSIRIS-REx and Hayabusa 2 missions.This work is partly funded by the Deutsche Forschungs- gemeinschaft (DFG, German Research Foundation) – Project-ID 263649064 – TRR 170 (A.B., C.B., T.K.); this is TRR170 Publication No. 119. M.S. and C.M. thank the Swiss National Science Foundation (SNF) for support. The work of H.B. and M.S. has been in parts carried out within the framework of the NCCR PlanetS supported by SNF. D.H. thanks F. Langenhorst for support and access to the FIB-SEM and TEM facilities at FSU-IGW, which are funded by the DFG via grant LA830/14-1. D.F. (CIW) acknowledges the support of the NASA awards 80NSSC19K0559 and 80NSSC20K0344

Radionuclide Release in Geothermal Aquifers -the Role of Alpha Recoil

ABSTRACT The concentration of Ra-226, Ra-228 and Ra-224 in geothermal brines is caused to a high extent by -recoil processes at the mineral/fluid interface in the aquifer. A Monte Carlo code for the prediction of the activity concentrations and the isotope ratios was developed and tested on single and multi component systems, respectively. The simulations consider the chemical behaviour of released recoil nuclei in the solution as well as the statistical character of the recoil process. Analytical data of Radium isotopes in a geothermal fluid of the North German Basin were well reproduced by this model. Highly radioactive fracture fillings in the granite of Soultz-sous-Forêts could be excluded as a source of the Radium concentration in the associated brine

MOESM1 of How well suited are current thermodynamic models to predict or interpret the composition of (Ba,Sr)SO4 solid-solutions in geothermal scalings?

Additional file 1: Figure S1. Geologic map of Mecklenburg-Vorpommern showing pre-quaternary formations. Highlighted with a blue triangle is the location of the geothermal site near Neustadt-Glewe. The map was downloaded from Environmental Geodata Services Mecklenburg-Vorpommern at: http://www.umweltkarten.mv-regierung.de/atlas . For more detailed information about the geothermal usability of the underground in Mecklenburg-Vorpommern, but also in Germany in general, we refer the reader to a brochure published by LIAG, which is available at: https://geotis.de/homepage/Ergebnisse/LIAG_Broschuere_Tiefe_Geothermie.pdf and contains a number of very informative maps. Table S1. Composition of the geothermal brine from Neustadt-Glewe (after ref. (Degering et al. 2009) from the main manuscript). For comparison the composition used for modelling (after ref. (KĂźhn et al. 1997) from the main manuscript) is given in the last column