International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Volume 71 no. 2 / April 2020

Volume 71 no. 2 / April 2020

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Articles in this issue

  • Hydrothermal mineralisation of the Tatric Superunit (Western Carpathians, Slovakia): I. A review of mineralogical, thermometry and isotope data

    Abstract: The Tatric Superunit of the Western Carpathians hosts many ore deposits and occurrences. Inspection of innumerable surface and underground outcrops, drill cores, and hand specimens in the past allowed to distinguish these mineralisation stages, ordered from the oldest to the youngest ones: molybdenite, scheelite, arsenopyrite–pyrite–gold, stibnite–sphalerite–Pb–Sb-sulfosalts, dolomite–baryte–tetrahedrite, siderite–ankerite, quartz–tourmaline, quartz– Cu-sulfide, galena–sphalerite, baryte, and hematite stages. This work gives a detailed account of the mineralogy, fluids, depth of formation, and stable isotope signatures of these stages, based on the extensive published and unpublished literature. The early molybdenite, scheelite, and arsenopyrite–pyrite–gold stages contain fluid inclusions with low-salinity (0–10 wt. % NaCl eq.), CO2-rich aqueous fluids. The homogenisation temperatures (TH) are 300–350 °C, in agreement with the results of arsenopyrite and chlorite geothermometry. Estimated formation depth is down to 12 km and stable isotopes (δ18O, δD) suggest a metamorphic source of the fluids and the genetic association with orogenic gold deposits. The voluminous stibnite–sphalerite–Pb–Sb-sulfosalts stage originated from aqueous fluids (with NaCl–KCl, below halite saturation), with traces or without CO2, and TH of 105–170 °C. This stage was concluded with precipitation of senarmontite, kermesite or other oxygen-bearing ores, suggesting increase of oxygen fugacity in the terminal phases of ore precipitation, and perhaps an influx of meteoric water. The rich assemblages of Sb minerals at the deposits in the Malé Karpaty Mts. allows to trace the evolution of the hydrothermal systems in the f O2–f S2–T space. The calculated δ18O fluid values for the siderite–ankerite stage may correspond to marine or formation waters influenced by the isotopic exchange with high-grade metamorphic rocks. The siderite–ankerite, galena–sphalerite and dolomite–baryte–tetrahedrite stages are related to NaCl–CaCl2 fluids, often supersatured with respect to halite at room temperature. Some fluid inclusions showed higher TH (230–290 °C), confirmed also by myrmekitic breakdown of meneghinite. Later fluids with TH of 120–170 °C were recorded at many localities of these stages.
  • Hydrothermal mineralisation of the Tatric Superunit (Western Carpathians, Slovakia): II. Geochronology and timing of mineralisations in the Nízke Tatry Mts.

    Abstract: Ore mineralisations from the Nízke Tatry Mts., assigned to a number of mineralisation stages, were dated in this work by U/Pb analysis by laser ablation–sector field–inductively coupled plasma–mass spectrometry (LA–SF–ICP–MS), Re/Os, chemical Th/U/total Pb isochron method (CHIME), and U–total Pb methods. The samples originated mostly from the large Dúbrava deposit, with additional samples from Magurka, Rišianka, Soviansko, and Malé Železné deposits and occurrences. Additional, mostly unpublished Re/Os, K/Ar, and Ar/Ar data are also considered and discussed. Uraninite from a granite pegmatite and molybdenite from quartz veinlets gave ages of 343±1 and ≈351 Ma, respectively, comparable to the ages of the host rocks. The previously published K/Ar datum on biotite from the scheelite stage (330±5 Ma) is interpreted as a cooling age and its relation to the ore mineralisation is not clear. The arsenopyrite–pyrite–gold stage was dated, although only at a single sample, to 320±8 Ma. The ages for the samples of the stibnite–sphalerite–Pb–Sb-sulfosalts stage scatter also around this date, showing that these mineralisations are late Variscan. It could be assumed that this stage formed during the life span of a fluid circulation system and the later precipitation of stibnite and sulfosalts is simply owing to the temperature dependence of Sb solubility in the fluids. Scattered K/Ar data on illite document the Jurassic continental rifting but seem to be linked to none of the hydrothermal stages. The dolomite–baryte–tetrahedrite stage formed during the post-rift thermal relaxation of the Tatric basement, with ages varying between 156±13 and 128±4 Ma. The quartz–tourmaline stage, devoid of ore minerals, formed during the mid-Cretaceous Alpine metamorphism, with the scattered data averaging to ≈100 Ma. The following compression of the Tatric and Veporic complexes is reflected in sparse U/Pb carbonate ages (72 Ma) and remobilisation of uranium mineralisation (70 Ma). The constraints on the age of the quartz–Cu-sulfide and galena–sphalerite stages are insufficient but their formation could be perhaps placed into uppermost Cretaceous. The vein carbonates were remobilised at 17–31 Ma, with most ages clustering around 24 Ma, related to the burial of parts of the Tatric basement under the Central Carpathian Paleogene Basin. This work documents many episodes of Variscan and Alpine hydrothermal activity that can be linked to the tectonothermal evolution of the Western Carpathians.
  • The first skeletal evidence of an Upper Triassic (Rhaetian) diapsid reptile from the Western Carpathians (Strážov Highlands, Slovakia)

    Abstract: Here we describe the first skeletal evidence of a tetrapod from Rhaetian (Upper Triassic) marine deposits of the Western Carpathians. The material consists of an isolated left femur and comes from the Úbočka locality near Čičmany in the Strážov Highlands. Based on morphological, histological, and stratigraphic evidence, we can exclude affinities of this femur to the most commonly occurring aquatic reptiles: the Eosauropterygia. The histology of a femur of aff. Pachystropheus from Aust Cliff, Gloucestershire, UK, is also described here for the first time and compared to the bone from Slovakia. However, a precise taxonomical assignment of the Rhaetian femur from Slovakia is not possible. The bone shows strong osteosclerosis that points to an inhabitant of a shallow marine environment. On the basis of morphological and histological characters, affinities to a cyamodontoid placodont, Endennasaurus-like thalattosaur or a rhynchocephalian are conceivable. The morphology of the Slovak find does not fully exclude choristoderan affinity, but the rare histological data available for comparison do not support such a statement. For all these reasons, we allocated this bone as Diapsida indet. The bone described here sheds the first, although limited light on the possible faunal composition of the Rhaetian tetrapod assemblage in the Western Carpathians. We can assume that the bone, which shows marks of transport, either represents an allochthonous component in this marine environment, transported postmortem and most likely from nearby dry land (i.e., in the case of rhynchocephalian affinities), or it belonged to an inhabitant of this shallow coastal biotope (e.g., cyamodontoid placodont affinities).
  • Petroleum potential of Middle Jurassic rocks in the basement of the Carpathian Foredeep (Ukraine) and oil-to-source correlation with oil in Upper Jurassic reservoirs

    Abstract: Organic matter-rich Middle Jurassic rocks occur in the Mesozoic basement of the Carpathian Foredeep in Ukraine. Eighty-nine core samples from the Mosty-2, Korolyn-6 and Korolyn-2 wells as well as three oil samples from the Kokhanivka and Orkhovychi oil fields in the Kokhanivka Zone, were investigated. Bulk geochemical data as well as maceral analysis have been determined, and a subset of these samples, including all oil samples, have been investigated for biomarker composition. Middle Jurassic strata are rich in organic matter (average: 4.19 wt. %) and reach TOC contents of up to 14.98 wt. %. However, HI values are low, typically around 100 mg HC/g TOC, and only reach a maximum of 242 mg HC/g TOC, indicating dominance of gas-prone, Type III kerogen. Tmax values as well as random vitrinite reflectance measurements for the Mosty-2 (434 °C; 0.69–0.71 % Rr), Korolyn-6 (443 °C; 0.78–0.82 % Rr) and Korolyn-2 (448 °C; 0.85–0.90 % Rr) wells indicate that thermal maturity increases with depth from marginally mature to mature, suggesting that hydrocarbon generation may have occurred. However, biomarker data suggests no genetic link between these rocks and Upper Jurassic oils, as C27–C28–C29 sterane distributions, Pr/Ph ratios, DBT/Phenanthrene ratios and isotope data display significant differences between the two. New geochemical data, along with published biomarker data on Upper Jurassic rocks and crude oils belonging to the same oil family as the Upper Jurassic oils in the Ukrainian Carpathians, showed that Upper Jurassic rocks from the Korolyn-6 well present a better fit and are the source for the analysed oils.
  • 40Ar/39Ar geochronology using high sensitivity mass spectrometry: Examples from middle Miocene horizons of the Central Paratethys

    Abstract: 40Ar/39Ar radio-isotopic dating of volcanic tuffs intercalated in sediments can provide high accuracy age control on the deposition of sedimentary rocks. State-of-the-art mass spectrometers such as the ARGUS VI+ are able to acquire highly precise ages for relatively small single grains (~90–250 μm for Miocene samples). Single grain measurement can provide insight into the sometimes complex age distributions within volcanic tuffs. The results show that 40Ar/39Ar ages based on multiple grain fusions will not necessarily reflect eruption ages, which can lead to (slight) overestimation of the depositional age. The paper compares multiple and single grain data from different Miocene tuffs in the Central Paratethys, which plays an important role in the establishment of a geological time frame for this area. The examples come from three middle Miocene tuff horizons that span from the Badenian transgression to the Badenian–Sarmatian Extinction Event. The new ages obtained from the Quellgraben section in the Styrian Basin (14.31± 0.27 Ma and 14.03 ± 0.04 Ma) are much younger than the previous dating and together with the new data from the Bernhardsthal-4 well, Vienna Basin (15.12 ± 0.19 Ma) indicate, that the Badenian (Langhian) marine flooding did not reach this area before 15.2 Ma. The new weighted mean age of 12.56 ± 0.10 Ma from the Kamenica nad Hronom section in the Danube Basin dates the transition from marine to terrestrial setting, which is possibly connected with a sea level lowstand at the beginning of the Sarmatian.
  • U–Pb zircon geochronology and geochemistry of the metamorphic sole rocks of the Meydan mélange, South-East Turkey: Implications for ophiolite emplacement and protolith

    Authors: NUSRET NURLU
    Abstract: Metamorphic sole rocks at the base of the mantle tectonites of the Meydan ophiolite in South-East Anatolia, Turkey, are directly overlain by sheared serpentinites and cut by unmetamorphosed mafic dikes. They are found in areas close to the forefront of the Tauride thrust and are described as biotite amphibole schist (Bt + Hbl + Act + Plg + Rt ± Zrn), prehnite–pumpellyite–amphibole schist (Prh + Pmp + Act + Plg ± Rt ± Ttn), amphibole schist (Fe2+– Act + Qtz + Plg ± Anl ± Zrn), and amphibolite (Mg–Hbl + Plg ± Zrn ± Rt). They are identified as island arc tholeiites (IATs) based on their major- and trace-element whole-rock chemistry and mineral composition. The mafic dikes intruding into the metamorphic sole rocks and mantle tectonites exhibit tholeiitic affinity (Nb/Y = 0.03–0.13) and are geochemically similar to island-arc basalts. The multiple elements, rare earth element (REE) trends, and related diagrams suggest that the mafic dikes were generated in a supra-subduction zone (SSZ) setting. Geothermobarometric examination based on the chemical compositions of the magnesio-hornblende in the amphibolites indicated that the pressure and temperature during the metamorphism were ~ 2.4 kbar (at depths of roughly 9 km) and ~ 630 °C, respectively. To elucidate the relationship and timing between the formation of the Meydan ophiolite and that of the metamorphic sole rocks, this paper presents new zircon U–Pb geochronological data from two samples of sole rocks, the ages of which are indicated to lie in the range of 81.4 ± 0.69 Ma to 85.4 ± 0.93 Ma (Santonian–Campanian). The precise U–Pb geochronology and the detailed petrographical and geochemical features of the metamorphic sole rocks and the protolith are evaluated to identify the tectonic environments of supra-subduction realms characterizing the South-Eastern Anatolian Orogenic Belt (SAOB). The metamorphic sole rocks were formed as a result of intra-oceanic thrusting during supra-subduction events in the basin throughout the closure of the SAOB in the Late Cretaceous.