Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.https://www.jgeosci.orgen-US https://www.jgeosci.org/img-system/jgeosci_cover.jpghttps://www.jgeosci.org Lis GP, Białek D, Al Ghifari S, Szuszkiewicz A, Schito A; Vol. 70, issue 1, pages 1 - 14
Raman spectroscopy was used to measure the thermal maturity of organic matter in widespread low-grade Ordovician and Silurian metasedimentary rocks of the Kaczawa Metamorphic Complex. The suitability of different Raman-based geothermometer formulations for estimating peak metamorphic temperatures in the studied rocks was evaluated. Among the tested geothermometers, the formulation based on the full width at half maximum of the D1 band, and the calculations performed with the IFORS software yielded most consistent results, reproducing with sufficient accuracy and reliability the peak metamorphic temperatures obtained by other authors. Disruptions in the regional temperature distributions due to thermal overprint caused by local volcanic activity were identified by studying the contact aureole around a large body of the Wielisławka Rhyolite. It was found that the influence of contact metamorphism on the measured spectral parameters becomes insignificant at about 150 m away from the contact. The regional distribution of peak temperatures not affected by late thermal overprinting shows a clear pattern with the record of higher temperatures preserved in the southern part of the Kaczawa Metamorphic Complex. Depending on the tectonic unit, peak temperatures vary from 312 to 352 °C, with an average of about 331 °C. Temperatures calculated for the units in the northern Kaczawa Metamorphic Complex branch range from 278 to 301 °C, with an average of 289 °C. With estimated geothermal gradient of 15 °C/km for the peak thermal conditions, the difference of 40 °C indicates the southern branch was buried 2.5-3.0 km deeper than the northern branch. ]]> https://www.jgeosci.org/rss.php?ID=jgeosci.401 Original paper https://www.jgeosci.org/rss.php?ID=jgeosci.401 Mészárosová N, Skála R; Vol. 70, issue 1, pages 15 - 31
Among enstatite-rich meteorites are included enstatite chondrites and enstatite achondrites (aubrites). The reducing conditions of origin are reflected in their mineralogy. Due to the lack of oxygen-bearing mineral assemblages allowing the application of traditional geothermometers, sulfides are used as a tool to constrain the conditions of their origin. In general, sulfide-based geothermometers rely on the contents of major or minor elements traditionally determined by electron probe microanalysis. This method requires the analyzed material to be a homogenous single phase in the analytical volume. However, sulfides of enstatite-rich meteorites frequently contain tiny lamellar inclusions of different phases, and therefore, the inclusions might affect the overall composition of sulfides. Consequently, the results of such analyses might influence the estimates of the conditions under which the given meteorite formed. This study discusses the effect of using the low-overvoltage approach to analyze iron and nickel (10 kV) in the primary sulfides of enstatite-rich meteorites and how results compare to those obtained with the traditional analytical protocol (20 kV). The sulfides analyzed included Cr-Ti-bearing troilite, daubréelite (FeCr₂S₄), and (Mg,Fe,Mn)S-monosulfide. Unfortunately, troilite often contains lamellar inclusion of daubréelite. Moreover, troilite inclusions are occasionally also included in (Mg,Fe,Mn)S-monosulfide. Therefore, obtaining an unbiased analysis of these minerals is intricate. Due to this, the main objective of using a lower accelerating voltage is to reduce the analytical volume to the minimum to increase the probability of avoiding tiny inclusions. Even if the analytical volume is inclusion-free, another complication might occur as the analysis of troilite may be affected by the neighboring daubréelite due to boundary fluorescence. Consequently, both phenomena bias the Cr content measured in troilite similarly, and due to the complexity of troilite-daubréelite assemblage, it is nearly impossible to quantify the amount of Cr content unbiased. Subsequently, to obtain the best possible dataset, precise sample screening and careful analytical point location setting are required in general. Using lower accelerating voltage brings many advantages as it allows better observation of the inclusions, and due to reducing the analytical volume, it reduces the chance of the presence of inclusions and suppresses the bias in Cr from boundary fluorescence. However, it also has disadvantages as the analysis is not trivial and does not favor trace elements analysis in general. Results demonstrate the importance of point-by-point inspection of the acquired data and subsequent elimination of biased analyses from the final datasets. ]]> https://www.jgeosci.org/rss.php?ID=jgeosci.402 Original paper https://www.jgeosci.org/rss.php?ID=jgeosci.402 Sejkora J, Biagioni C, Dolníček Z, Voudouris P; Vol. 70, issue 1, pages 33 - 42
Arsenogoldfieldite is a new mineral discovered in a sample collected from the North Star mine, Mammoth, Tintic district, Juab County, Utah, U.S.A (type locality). It occurs as anhedral grains, up to 300 μm in size, in a quartz gangue, associated with tellurium, enargite including Sn-bearing variety and supergene juabite. Arsenogoldfieldite is black, with a metallic luster. Mohs hardness is ca. 3½-4; calculated density is 4.954 g.cm^-3. In reflected light, arsenogoldfieldite is grey with a brownish shade; it is isotropic. Internal reflections were not observed. Reflectance values for the four COM wavelengths in air [R (%) λ (nm)] are: 30.2(470); 29.9(546); 29.9 (589); and 30.4 (650). The empirical formula of arsenogoldfieldite is Cu_11.75Zn_0.03Fe_0.02[(As_1.44Sb_0.43Bi_0.13)_Σ2.00Te_2.00]S_13.11. The ideal formula is Cu₁₂(As₂Te₂)S₁₃, which requires (in wt. %) Cu 48.13, As 9.46, Te 16.11, S 26.30, total of 100.00. Arsenogoldfieldite is cubic, I-43m, with unit-cell parameters a = 10.2868(4) Å, V = 1088.53(13) ų, Z = 2. The strongest reflections of the X-ray powder diffraction pattern [d, Å (I) hkl] are: 3.638 (8) 220, 2.969 (100) 222, 2.573 (9) 400, 1.8187(21) 440 and 1.5504(9) 622, According to the single-crystal X-ray diffraction data (R = 0.0221 on the basis of 380 unique reflections with F_o > 4σF_o and 22 refined parameters), arsenogoldfieldite is isotypic with other tetrahedrite-group minerals. Arsenogoldfieldite is named in agreement with the nomenclature of the tetrahedrite group as the (As/Te) end-member in the goldfieldite series. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (2022-084). The description of arsenogoldfieldite from the Pefka mine, Alexandroupoli, Western Thrace, Greece (cotype locality), its chemical composition and crystal structure data are also given in the paper. ]]> https://www.jgeosci.org/rss.php?ID=jgeosci.0034.25 Original paper https://www.jgeosci.org/rss.php?ID=jgeosci.0034.25