Stable isotope evidence for near-surface, low-temperature formation of Mg-(hydro)carbonates in highly altered Greek Mesozoic serpentinites

Authigenic magnesite, hydromagnesite and huntite associated with intensely altered and serpentinized ophiolitic rocks in Attica (mainland Greece) occur predominantly as veinlets and nodules within a totally weathered former-serpentinite groundmass. Carbonate δ18O values are consistent with post-geothermal fluid temperatures between 25-70 ˚C, but mostly between 25-30 ˚C, from a dominantly meteoric-sourced groundwater, indicating near-surface, low-temperature conditions. Despite the proximity of a volcanic centre with strong CO2 flux, 75% of the carbon isotope data imply little or no incorporation of this CO2 into the authigenic Mg-(hydro)carbonates. Indeed, many δ13C values are more negative than soil-zone calcrete values, and in this setting Mg-(hydro)carbonate δ13C below -6‰ VPDB probably indicate disequilibrium effects in alkaline groundwaters. Geothermal fluids and groundwaters were mainly routed through structural conduits. Some of the low temperature hydromagnesite subsequently dehydrated to magnesite under near-surface conditions, while huntite is likely a diagenetic transformation of hydromagnesite, forming close to the volcanic centre where fluid Mg/Ca ratios were low. The isotopic signatures are distinct from previously published Balkan-East Mediterranean magnesite data arrays but are consistent with many other ultramafic-associated magnesium carbonates worldwide; their association with likely fluid compositions provide important context for Mg-(hydro)carbonate formation as geothermal conditions cool to near surface temperatures

A new Ni-rich stevensite from the ophiolite complex of Othrys, Central Greece

The first occurrence of Ni-rich stevensite found in the ophiolite complex of Othrys, Central Greece is described. The stevensite, which develops in cracks in a host serpentinite, formed at the expense of serpentine. Two varieties of stevensite have been described: a Mg-rich, Ni-poorer variety with 0.4-1.2 octahedral Ni atoms per half formula unit (p.h.f.u.) and a Ni-rich variety with >2 Ni atoms p.h.f.u. The layer charge in both varieties is -0.24 p.h.f.u.. Stevensite layers are completely separated when dispersed in dilute polyvinylpyrrolidone (PVP) solutions and begin to convert to talc after heating at 250°C for 90 min. Total conversion to talc is observed at 550°C. Formation of Ni-rich stevensite took place at ambient temperature during supergene processes. The scarcity of Ni-rich stevensite occurrences in nature is attributed to the metastability of smectite and to the analytical procedures used in previous studies. Stevensite is considered a phase containing domains with variable numbers of octahedral vacancies. A new experimental protocol is proposed for the determination of Ni-rich stevensite, based on a combination of XRD after solvation with various organic liquids and subsequent heating at 750°C

Factors Controlling the Chromium Isotope Compositions in Podiform Chromitites

The application of Cr isotope compositions to the investigation of magmatic and post-magmatic effects on chromitites is unexplored. This study presents and compiles the first Cr stable isotope data (delta Cr-53 values) with major and trace element, contents from the Balkan Peninsula, aiming to provide an overview of the compositional variations of delta Cr-53 values in ophiolite-hosted chromitites and to delineate geochemical constraints controlling the composition of chromitites. The studied chromitites exhibit delta Cr-53 values ranging from -0.184 parts per thousand to +0.159 parts per thousand, falling in the range of so-called “igneous Earth” or “Earth’s mantle inventory” with values -0.12 +/- 0.11 parts per thousand to 0.079 +/- 0.129 parts per thousand (2sd). A characteristic feature is the slightly positively fractionated delta Cr-53 values of all chromitite samples from Othrys (+0.043 +/- 0.03 parts per thousand), and the occurrence of a wide range of delta Cr-53 values spanning from positively, slightly negatively to the most negatively fractionated signatures (Pindos, delta Cr-53 = -0.147 to +0.009 parts per thousand; Skyros, delta Cr-53 = -0.078 to +0.159 parts per thousand). The observed negative trend between delta Cr-53 values and Cr/(Cr + Al) ratios may reflect a decrease in the delta Cr-53 values of chromitites with increasing partial melting degree. Alternatively, it may point to processes related to magmatic differentiation, as can be seen in our data from Mikrokleisoura (Vourinos)

EVALUATING THE EFFICIENCY OF NATURAL AND SYNTHETIC ZEOLITIC MATERIALS FOR THE REMEDIATION OF POLLUTED MINING SOILS: A COMPARATIVE STUDY

The aim of this study is to examine the effectiveness of natural and synthetic zeolitic materials as potential soil amendments for the rehabilitation of mine degraded areas. Thus, heavily polluted soil was sampled from the Lavrion mining district in Greece. Two types of natural zeolite tuffs, clinoptilolite- and mordenite-rich, originating from Samos Island, Greece, were pulverized in the laboratory and used as low cost modifiers. Furthermore, a lignite-derived fly ash bulk sample collected from the electrostatic filters of the Meliti Lignite fired Power Station, west Macedonia, Greece, was modified by a low temperature alkaline hydrothermal treatment. The end product was the zeolite Na-P1 (Na6Al6Si10O32•12H2O), which is characterized by its high CEC capacity. Mixtures composed of 90% contaminated soil and 10% w/w of each of the three zeolitic materials were produced for analysis and tests. XRD and SEM methods were used for the characterization of the raw materials and the end-products. Estimation of water solubility and potential bioavailability with the EDTA extracting agent of heavy metals (Pb, Zn, Cu, Mn, Fe, Cd) was performed in those soil mixtures, following the with the European standard EN 12457-2. Furthermore, pot experiments that were implemented revealed that all three zeolite-bearing amendments, have successfully decrease the potentially toxic elements uptake by the Trifolium alexandrinum crop. Soil mixtures containing synthetic zeolitic materials have displayed pH regulation, higher cation exchange capacity values, excellent growth of T. alexandrinum, as well as, a decrease of heavy metals content within the plant tissue. The results of the present study demonstrated that the fly ash synthesized zeolitic material exhibited the best results not only in the regulation of pH, in the increase of CEC, in the growth of T. alexandrinum, but also in reducing of potential bioavailability and water solubility of all 6 potentially toxic elements studied

On the Origin of Bastnaesite-(La,Nd,Y) in the Nissi (Patitira) Bauxite Laterite Deposit, Lokris, Greece

A detailed geochemical study and a thorough mineralogical description of the rare-earth elements (REE)-minerals and associated minerals were carried out in two vertical profiles of approximately 4 m length, from the Nissi (Patitira) bauxite laterite deposit, Lokris, Greece, characterized by the presence of goethite in small sizes resembling bacterial cell coated by goethite and a significant REE enrichment. The enrichment of the REE concentrated in bastnaesite-group minerals, the intergrowths between REE-minerals and Al–Ni–silicates with significant sulfur contents and their association with goethite microtextures interpreted as bacteriomorphic, indicate REE remobilization along with iron bio-leaching and re-precipitation on karstified limestone. In addition to the previous-reported hydroxylbastnaesites, a (La,Nd,Y)(CO3)F member of the bastnaesite-group associated with Al–Ni–silicates were identified, the stability of which may reflect the dependence on the source rocks and the local variations of pH-Eh. Interaction between downward percolating water and carbonate rocks seems to be a very effective mechanism for REE fluorocarbonates deposition under alkaline and reducing conditions

Comparing Methods for Parameter Estimation of the Gompertz Tumor Growth Model

Available: https://doi.org/10.1016/j.ifacol.2017.08.2289International audienceCancer, also known as malignant tumor or malignant neoplasm, is the name given to a collection of related diseases. In all types of cancer, some of the body's cells begin to divide abnormally without stopping and have the potential to invade surrounding tissues. In this work, we focus on estimating the parameters of a model which tries to describe the growth of a cancer tumor based on the available measurements of the tumor volume and on comparing the effectiveness with respect to the accuracy of the estimation of the various methods we have tested. The Gompertz function is used as the model basis, and our analysis aims to compute the growth rate and the plateau size of the tumor. The methods used to estimate these parameters are based on least squares, maximum likelihood and the Extended Kalman Filter (EKF). In this work, we present five different methods. The results show that, when the process and measurement noise characteristics are known, maximizing the joint probability density function of the observations using numerical integration to compute the probability density functions yields most times the best results. The methods based on the EKF also yield satisfactory results