Hydrotermální karbonáty a termometrie žilné mineralizace v terciérních vulkanitech u Uherského Brodu

Hydrothermal mineralization in the Bučník quarry near Uherský Brod is the best locality for the study of this type of mineralization in the Outer Western Carpathians. The studied sulfide vein mineralization is genetically linked to Tertiary volcanics and represents a distance manifestation of the same vein type in the metallogenetic region of the Central Slovakian Volcanic Field.Study of vein structure, ore textures and structures, chemical composition of carbonates, isotope thermometry (isotopic composition of sulfur sphalerite/galena) and fluid inclusions, including microthermometry, shows that mineralization occurred under complex and variable conditions. Carbonates, defined as calcites with a proportion of Fe and Mn, dolomites and Fe- and Mn-dolomites, Mg-ankerites, show a highly variable chemical composition clearly documented as fine zones in CL-microscopy and BSE images.Fluid inclusions contain the aqueous system H2O-NaCl and H2O-NaCl + MgCl2 + FeCl2-3. Fluid salinity ranges from 2.7 to 14.7 mass% NaCl eq. whereas it is higher for sphalerite than for carbonates. The same trend is for homogenization temperatures in the range of 121-272 °C.Isotopic thermometry in combination with microthermometry shows a relatively wide probable range of temperature conditions. The younger carbonate mineralization may begin at temperatures of 125 °C and around 200 °C may overlap with a temperature of sulfide association that ranges from 170 °C to 335 °C. Isotopic thermometry also suggests possible higher temperatures up to 450 °C and above, but these highest temperatures are rather unlikely. The wide temperature range in which the mineralization originated is in accordance with the development of the hydrothermal system in a very dynamic environment in terms of tectonic, magmatic and hydrothermal. The studied hydrothermal system has a number of physico-chemical parameters similar to vein systems in the Central Slovakian volcanics region

Isotope diffusion and re-equilibration of copper and evaporation of mercury during weathering of tetrahedrite in an oxidation zone

To understand the mobility of heavy metals during oxidative weathering of sulfides, we investigated weathering processes of tetrahedrite [(Cu,Fe,Zn,Hg)12(Sb,As)4S13] in an oxidation zone with abundant siderite (FeCO3) and baryte (BaSO4) at Rudňany (Slovakia). The focus of this work lied in the isotopic (δ65Cu, δ202Hg, δ34S) variations of the minerals during weathering and the interpretation of such changes. In the studied oxidation zone, Hg-rich tetrahedrite converts in situ to pockets of powdery cinnabar (HgS) and an X-ray amorphous mixture rich in Sb, Fe, and Cu that slowly re-crystallizes to Cu-rich tripuhyite (FeSbO4). Copper is mobile and precipitates as malachite [Cu2(OH)2(CO3)], azurite [Cu3(OH)2(CO3)2], or less abundant clinoclase [Cu3(AsO4)(OH)3]. The isotopic composition (δ65Cu) of tetrahedrite correlates well with the degree of weathering and varies between 0.0 ‰ and −4.0 ‰. This correlation is caused by isotopic changes during dissolution and subsequent rapid equilibration of δ65Cu values in the tetrahedrite relics. Simple diffusion models showed that equilibration of Cu isotopic values in the tetrahedrite relics proceeds rapidly, on the order of hundreds or thousands of years. Abundant secondary iron oxides draw light Cu isotopes from the aqueous solutions and shift the isotopic composition of malachite and azurite to higher δ65Cu values as the distance to the primary tetrahedrite increases. Clinoclase and tripuhyite have lower δ65Cu values and are spatially restricted near to the weathering tetrahedrite. The Hg and S isotopic composition of tetrahedrite is δ202Hg = −1.27 ‰, δ34S = −1.89 ‰, that of the powdery secondary cinnabar is δ202Hg = +0.07 ‰, δ34S = −5.50 ‰. The Hg isotopic difference can be explained by partial reduction of Hg(II) to Hg(0) by siderite and the following evaporation of Hg(0). The S isotopic changes indicate no involvement of biotic reactions in the oxidation zone, probably because of its hostility owing to high concentrations of toxic elements. This work shows that the Cu isotopic composition of the primary sulfides minerals changes during weathering through self-diffusion of Cu in those minerals. This finding is important for the use of Cu isotopes as tracers of geochemical cycling of metals in the environment. Another important finding is the Hg in the oxidation zones evaporates and contributes to the global cycling of this element through atmospheric emission

Porosity Development Controlled by Deep-Burial Diagenetic Process in Lacustrine Sandstones Deposited in a Back-Arc Basin (Makó Trough, Pannonian Basin, Hungary)

Deeply buried Pannonian (Upper Miocene) siliciclastic deposits show evidence of secondary porosity development via dissolution processes at a late stage of diagenesis. This is demonstrated by detailed petrographic (optical, cathodoluminescence, fluorescence, and scanning electron microscopy) as well as elemental and stable isotope geochemical investigations of lacustrine deposits from the Makó Trough, the deepest depression within the extensional Pannonian back-arc basin. The analyses were carried out on core samples from six wells located in various positions from centre to margins of the trough. The paragenetic sequence of three formations was reconstructed with special emphasis on sandstone beds in a depth interval between ca. 2700 and 5500 m. The three formations consist, from bottom to top, of (1) open-water marls of the Endrőd Formation, which is a hydrocarbon source rock with locally derived coarse clastics and (2) a confined and (3) an unconfined turbidite system (respectively, the Szolnok and the Algyő Formation). In the sandstones, detrital grains consist of quartz, feldspar, and mica, as well as sedimentary and metamorphic rock fragments. The quartz content is high in the upper, unconfined turbidite formation (Algyő), whereas feldspars and rock fragments are more widespread in the lower formations (Szolnok and Endrőd). Eogenetic minerals are framboidal pyrite, calcite, and clay minerals. Mesogenetic minerals are ankerite, ferroan calcite, albite, quartz, illite, chlorite, and solid bituminous organic matter. Eogenetic finely crystalline calcite yielded δ13CV−PDB values from 1.4 to 0.7‰ and δ18OV−PDB values from –6.0 to –7.4‰, respectively. Mesogenetic ferroan calcite yielded δ13CV−PDB values from 2.6 to –1.2‰ and δ18OV−PDB values from –8.3 to –14.0‰, respectively. In the upper part of the turbidite systems, remnants of the migrated organic matter are preserved along pressure dissolution surfaces. All these features indicate that compaction and mineral precipitations resulted in tightly cemented sandstones prior to hydrocarbon migration. Interconnected, secondary, open porosity is associated with pyrite, kaolinite/dickite, and postdates of the late-stage calcite cement. This indicates that dissolution processes took place in the deep burial realm in an extraformational fluid-dominated diagenetic system. The findings of this study add a unique insight to the previously proposed hydrological model of the Pannonian Basin and describe the complex interactions between the basinal deposits and the basement blocks

Ocean acidification during the early Toarcian extinction event : evidence from boron isotopes in brachiopods

This project was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement and project BASE-LiNE Earth (643084) and by the Slovak Research and Development Agency (APVV17-0555) and the Slovak Scientific Grant Agency (VEGA 0169/19).The loss of carbonate production during the Toarcian Oceanic Anoxic Event (T-OAE, ca.183 Ma) is hypothesized to have been at least partly triggered by ocean acidification linkedto magmatism from the Karoo-Ferrar large igneous province (southern Africa and Antarctica).However, the dynamics of acidification have never been directly quantified across theT-OAE. Here, we present the first record of temporal evolution of seawater pH spanning thelate Pliensbachian and early Toarcian from the Lusitanian Basin (Portugal) reconstructedon the basis of boron isotopic composition (δ11B) of brachiopod shells. δ11B declines by ~1‰across the Pliensbachian-Toarcian boundary (Pl-To) and attains the lowest values (~12.5‰)just prior to and within the T-OAE, followed by fluctuations and a moderately increasingtrend afterwards. The decline in δ11B coincides with decreasing bulk CaCO3 content, inparallel with the two-phase decline in carbonate production observed at global scales andwith changes in pCO2 derived from stomatal indices. Seawater pH had declined significantlyalready prior to the T-OAE, probably due to the repeated emissions of volcanogenicCO2. During the earliest phase of the T-OAE, pH increased for a short period, likely dueto intensified continental weathering and organic carbon burial, resulting in atmosphericCO2 drawdown. Subsequently, pH dropped again, reaching the minimum in the middle ofthe T-OAE. The early Toarcian marine extinction and carbonate collapse were thus driven,in part, by ocean acidification, similar to other Phanerozoic events caused by major CO2 emissions and warming.Publisher PDFPeer reviewe

Mg/Ca ratios and foraminiferal stable isotopes of sediment core LOM-1, Lomnice, Czech Republic

Details regarding seawater temperature and isotopic composition of seawater in the Central Paratethys, during the Miocene epoch, are not well known. Here we present an insight based on results from a combination of Mg/Ca, δ18O and δ13C on foraminifera from the shallow core (LOM-1) representing the time interval of ~ 14.4 to 14.36 Ma. Globigerinoides trilobus, Globigerina bulloides, Cibicidoides spp. and Melonis pompilioides were chosen for analysis due to their variable ecological preferences within the water column and on the sea floor. We assessed problems concerning diagenetic alteration of foraminiferal calcite by using a single test approach when analysing δ18O and δ13C. Paleotemperature ranges turned out to be comparable with modern subtropical regions with no cooling trend as was expected at this period following the Middle Miocene Climatic Optimum. However, we find an interesting offset between the benthic species temperature response that is likely related to the different life-strategies of those species. Based on a combination of mentioned proxies it was possible to partly reconstruct δ18Oseawater for the studied locality and compare it with Mg/Ca derived temperature to obtain a possible correlation between temperature and salinity. We also investigated differences in surface and bottom water hydrography in comparison with the Mediterranean, and distinguish their different hydrographies. In addition, it was possible to identify dissimilar origins of surface and bottom water masses based on comparison of their isotopic composition