Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Editorial ]]> Rapprich V; Vol. 69, issue 1, page: 1
As a new Editor in Chief, and after for our Journal somewhat hectic year 2023, I would like to welcome all our readers in the new year 2024, and wish them all the best. You are now browsing the first issue of the volume 69 (2024), which collects four interesting contributions focused on gold–silver mineralization related to the Štiavnica stratovolcano, late Ordovician magmatism in the Mongolian Gobi Altai Zone, interactions between melt and dunite from Mirdita ophiolite in Albania, and revision of the application of the 2Q–(Or + Ab)–4An (QUORAA) classification diagram, respectively. I believe that you will be gratified and inspired by this new portion of scientific reading. ]]> Editorial
<![CDATA[ Mineralogy and evolution of the epithermal mineralization in the Rudno nad Hronom-Brehy ore deposit, Štiavnické vrchy Mts. (Slovakia) ]]> Vlasáč J, Mikuš T, Majzlan J, Števko M, Biroň A, Szczerba M, Milovský R, Žitňan P; Vol. 69, issue 1, pages 21 - 47
The Rudno nad Hronom-Brehy ore deposit in Slovakia represents an important locality of epithermal precious metal mineralization in the Central Slovak Volcanic Field. The main ore structures in the area are Anna, Goldschram, Filip, Johan de Deo and Priečna veins. In this work, we present mineralogical, paragenetic and geochemical aspects of the ore mineralization, hydrothermal alteration patterns, fluid inclusions, isotopic composition of sulfur (δ 34S) and K-Ar age of ore mineralization. Four mineralization stages were recognized, the third one being split into two substages. (1) Pyrite stage with quartz, K-feldspar, arsenopyrite and pyrite. (2) Base-metal stage with sphalerite, galena, chalcopyrite, Au-Ag alloys and famatinite. (3a) Early Ag stage with tetrahedrite-(Zn), tetrahedrite-(Fe), argentotetrahedrite-(Zn), tetrahedrite-(Cd), argentotetrahedrite-(Cd) and greenockite. (3b) Late Ag stage with pyrargyrite, polybasite, pearceite, cupropolybasite, cupropearceite, acanthite and galena. (4) Late Ag-Cu stage with bornite, stromeyerite, mckinstryite, chalcocite, digenite, covellite and uytenbogaardtite. Veins are rich in silver with an average Ag : Au ratio of 85 : 1; in some parts of the veins, Ag content reaches up to 1950 ppm and Au up to 42.7 ppm. The neutral to alkaline style of hydrothermal alteration is represented by K-feldspar, quartz, carbonates, smectite, interstratified illite/smectite, and chlorite (clinochlore, chamosite). This assemblage indicates a low sulfidation origin of the mineralization formed at 177-224 °C. The δ34S values from the base-metal stage varies from +2.8 to +3.5 ‰ for chalcopyrite from the northern part of the Priečna vein, from +1.9 to +2.6 ‰ for galena, from +4.9 to +5.2 ‰ CDT for pyrite from the Anna vein. These values indicate a relatively homogeneous sulfur source, most likely related to an igneous or mixed igneous and host-rock source. Fluid inclusions in quartz associated with the base-metal stage have low salinity (1.1-1.6 wt. % NaCl eq.) and homogenization temperatures of 176-250 °C. The available data suggest that the base-metal stage was accompanied by cooling and dilution owing to a meteoric fluid. The temperature estimated from the tetrahedrite thermometer of the early Ag stage is ˜170-205 °C. According to the paragenetic relationship and mineral stability, the deposition temperatures in the late Ag stage did not exceed 160 °C. The late Ag-Cu stage formed at temperatures of <93 °C. The results of K-Ar radiometric dating from the hydrothermal alteration returned an average age of 12.5±0.3 Ma. The studied mineralization is possibly related to the initial stage of resurgent horst tectonic activity and rhyolite volcanism of the fifth stage of Štiavnica stratovolcano formation. ]]> Original paper
<![CDATA[ Late Ordovician magmatic pulse in the Tugrug Group, the Gobi Altai Zone, SW Mongolia ]]> Hanžl P, Uhrová L, Hrdličková K, Schulmann K, Buriánek D, Gansukh O, Míková J; Vol. 69, issue 1, pages 31 - 19
The Mongolian Altai Domain of the Central Asian Orogenic Belt is formed by a giant Lower Palaeozoic accretionary wedge that was later thrust over the northerly Central Mongolian Microcontinent. This accretionary complex mainly consists of late Cambrian-Ordovician volcano-sedimentary rocks represented by various formations within the Tugrug Group which were deformed, metamorphosed and intruded by numerous plutons during the Devonian-Carboniferous orogenic events. In this work, we report new U-Pb zircon ages of two felsic igneous rocks indicating an existence of the so far neglected Late Ordovician magmatic event affecting the Mongolian Altai accretionary wedge. The felsic volcanic sheet inside the upper part of the Tugrug Group in the western Gobi Altai Zone (eastern part of the Mongolian Altai Domain) yields an age of 457 ± 2 Ma and nearby granite pluton intruding the entire volcano-sedimentary sequence gives an age of 445 ± 1 Ma. Both rocks are high-K calc-alkaline, peraluminous, with similar geochemical patterns characterised by enrichment in mobile lithophile elements over Nb, Ti, P and Sr and nearly identical REE trends. All together, these features point to an analogous volcanic-arc-related magma source. This magmatism reflecting terminal stages of the accretionary wedge formation in the Mongolian Altai Domain may be related to the recently proposed Late Ordovician orogenic event. ]]> Original paper
<![CDATA[ Melt-rock interaction as a factor controlling evolution of chromite and olivine in dunite - case study from the Kukes Massif (Mirdita ophiolite, Albania) ]]> Mikrut J, Matusiak-Małek M, Ceuleneer G, Grégoire M, Onuzi K; Vol. 69, issue 1, pages 49 - 64
The ultramafic Kukes Massif is located in the eastern part of the Mirdita ophiolite (N Albania), which is recognised as representing Supra-Subduction lithosphere. It comprises a thick (0.8-2.5 km) dunite zone containing abundant occurrences of chromite ores and is cut by orthopyroxenitic and clinopyroxenitic veins. In this paper we focus on the genesis and evolution of olivine and chromite forming dunite in the northern part of the Kukes Massif. The chemical composition of minerals in dunites is highly variabile and apparent at outcrop scale. The most significant changes are recorded by olivine, which contains over 90 Fo in the host dunite but decreases to 87.5 in proximity of clinopyroxenitic veins. The composition of spinel is also sensitive to the presence of veins: in host dunite its Cr# is over 80 (chromite type I), whereas the presence of veins causes its decrease to 68 (type II). Clinopyroxene in vein-forming clinopyroxenite has Mg# from 86 to 92 and is Al-rich (Al2O3 0.8-2.6 wt. %). Orthopyroxene forms orthopyroxenites (Mg# 90-93, Al2O3 0.2-1.6 wt. %), but also screens (Mg# 83-91, Al2O3 0.8-2.4 wt. %) at the contact between clinopyroxenite veins and the host dunite.
The thick dunitic sequence at Kukes must have been formed as a result of intensive percolation of possibly boninitic melt through parental harzburgite. Another step in the evolution of the Kukes massif was related to intrusion of the pyroxenitic veins. These melts were not equilibrated with the host dunite and led to metasomatic modification of chromite and olivine, increasing Al2O3 content in former (from 6-8 up to 18 wt. %) and decreasing Fo (extremely from 92 to 87.5) in the latter. The process is evident proximal to clinopyroxenite veins, but a subtle effect is also recorded in the chemical composition of dunite contacting orthopyroxenite, leading to increase in Fe2O3 content. Metasomatism modified the composition of dunites in a zone of 0.5 m around pyroxenites. Our studies indicate a multistage evolution of the SSZ peridotites and show that its deciphering requires careful mineralogical examination. ]]> Original paper
<![CDATA[ The 2Q-(Or + Ab)-4An (QUORAA) diagram: poor for classification but good at deciphering the evolution of granitoids ]]> Sun M-M, Wang Y; Vol. 69, issue 1, pages 65 - 75
The 2Q-(Or + Ab)-4An (QUORAA) diagram (Enrique 2018) is proposed as an approximation of the modal QAP naming scheme for silica-saturated plutonic rocks. However, whether this scheme can reasonably reproduce the modal QAP classification results still needs to be tested. Through the inspection based on a dataset of 955 pairs of the mineral mode and whole-rock chemical compositions from the literature, it was found that the ratio of consistency between the two schemes is only 63.56 %. The consistency ratio is higher for discrimination of the granites (s.s.), but the inconsistency increases significantly for the rocks containing more mafic minerals (M > 25 %). As a section of the An-Ab-Or-Q (haplogranodiorite) tetrahedron, the QUORAA diagram is very helpful to illustrate the evolutionary paths of granitoid melts. The typical arc-related (ACG + ATG), the collision-related peraluminous (CPG + MPG), the rift-related peralkaline (PAG) as well as the potassic KCG granitoids show different trajectories in the QUORAA diagram. It is concluded that the QUORAA diagram would be applicable as a petrogenetic tool rather than the classification scheme. ]]> Original paper