Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US http://www.jgeosci.org/img-system/jgeosci_cover.jpghttp://www.jgeosci.org Dolníček Z, Ulmanová J, Havlíček J, Malý K, Jačková I; Vol. 68, issue 4, pages 261 - 280
A subvertical NW-SE trending fluorite-bearing vein at Bartoušov cut small body of two-mica granites hosted by high-grade metamorphic rocks of the Moldanubian Zone of the Bohemian Massif, in the northern part of the tectonic structure of the Jihlava Graben. The vein mineralization features open-space filling and multiple episodes of mineral precipitation. Early fine-grained quartz containing rare Nb- and W-enriched rutile is overgrown by crystals of late quartz and greenish to violet fluorite, followed by veinlets of dolomite-ankerite and calcite with pyrite and siderite. Quartz and fluorite crystallized from heterogeneous aquo-carbonic fluid with highly variable both bulk density and composition. Early CO₂-dominated aquo-carbonic fluids probably represent local retrograde-metamorphic fluids, whose variations in density likely reflect the pressure decrease during uplift of the basement during the Carboniferous. Late N₂-dominated low-density aquo-carbonic fluids were trapped at ˜135-150 °C and ˜60-100 bars. Raman analysis proved minor occurrence of CH₄, C₂H₆, H₂, and/or O₂ in the N₂-rich carbonic fluid. The composition of N₂-dominated carbonic fluid cannot be explained by the local basement sources only, but it could be derived from the now eroded immature Permo-Carboniferous sediments of the Jihlava Graben. In this concept, N₂, hydrocarbons, and possibly some H₂ could have been formed due to thermal alteration of immature organic matter, whereas O₂ and rest of H₂ were likely formed due to radiolysis of water within bodies of synsedimentary uranium ores present in this sedimentary basin. The infiltration of basinal fluids into basement was allowed due to an extensional tectonic regime. Paragenetically late carbonates originated from low- to moderate-salinity aqueous fluids derived from meteoric water and containing elevated amount of carbon from the oxidized organic matter. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.379 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.379 Žák K, Ackerman L, Veselovský F, Pašava J, Dobeš P, Svojtka M, Creaser RA; Vol. 68, issue 4, pages 281 - 299
A small and isolated hydrothermal vein-type Sb deposit is hosted by a lamprophyre dike which penetrated Neoproterozoic to early Cambrian volcanosedimentary successions near Chříč in the Teplá-Barrandian Unit, Czech Republic. Hydrothermal minerals were formed in several consecutive mineralization stages, separated by long pauses in hydrothermal fluid flow. Early Stage I is characterized by the formation of carbonates of dolomite-ankerite series (Carb I) and arsenopyrite with an imprecise Re-Os age of ˜570 to 510 Ma. Stage I was followed by tectonic movements and brecciation. The second mineralization stage (Stage II) is characterized by the precipitation of quartz (Qtz I) and Sb minerals (predominantly stibnite) while the third stage (Stage III) is marked by the presence of carbonates of dolomite-ankerite series (Carb II) and quartz (Qtz II) along with Cu, Zn, Pb, Ag and Fe sulfides. Lead isotope data of galena indicate a Variscan age of Stages II-III. These stages were followed by precipitation of another generation of carbonate of dolomite-ankerite series (Carb III, Stage IV), quartz (Qtz III, Stage V) and formation of Sb supergene minerals. The earlier reported occurrence of gold was not confirmed in the studied rock samples but three types of gold particles of variable fineness, with one of them indicating a local origin, were found in the heavy mineral concentrate from a local creek. Elevated Au concentrations were found in arsenopyrite and pyrite. The ore-forming hydrothermal fluid of the mineralization stage III was of H₂O-CO₂ type with minor CH₄ admixture, medium salinity, and temperatures in the range of 258-350 °C with an observed temperature decrease from Stage II to Stage V. Oxygen isotope data of Carb II correspond to high δ¹⁸O_fluid values (˜ +7.5 ‰ VSMOW) with a decrease in the fluid δ¹⁸O to later stages. An important part of the carbonate carbon was derived from decomposition of organic matter or its high-temperature reaction with hydrothermal fluid. Considering the wide variation in δ³⁴S values of sulfides and elevated Sb contents in the TBU black shales, we anticipate that the origin of the Chříč mineralization is closely associated with a metal and carbon-sulfur remobilization from the TBU volcanosedimentary successions in response to Cadomian and Variscan tectonothermal events. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.381 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.381 Bermanec M, Chukanov NV, Varlamov DA, Rajačič A, Jančev S, Ermolaeva VN; Vol. 68, issue 4, pages 301 - 311
A specific feature of a major part of regional metamorphosed metasomatic ores of the Nežilovo area, Pelagonian massif, Republic of North Macedonia is the occurrence of chalcophile elements (Zn, Pb, Sb, Cu, and As) in oxides and oxysalts whereas sulfides and sulfosalts are absent. This paper describes anomalous sulfide-bearing mineral assemblage discovered in small, localized outcrops at the Kalugeri locality belonging to the Nežilovo group of ore occurrences. Based on the data on mineral assemblages and associations, a four stage model is proposed. Pressures of the first stage was estimated to be above 20 kbar using barometry on Ba-rich first generation of phengite and temperatures above 530 °C were estimated by Zr in rutile thermometer. During this stage, sulfide mineralization still occurs with crystallization of sphalerite and galena. In the second stage occurring above 500 °C and above 10 kbar, the first generation of cymrite crystallized showing that barium was present in the system in excess compared to sulfur. The third stage was dominated by Zn-rich phengite, baryte-anglesite solid solution and cerussite formation at temperatures between 500 and 350 °C and pressures between 7.1 and 4 kbar. The final stage of formation is characterized by crystallization of the second generation of cymrite below 350 °C. It is concluded that sulfide-free ores of the Nežilovo type could form as a result of transformation of initial sulfide ores at low-PT conditions and a high barium activity. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.383 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.383 Myšľan P, Števko M, Mikuš T; Vol. 68, issue 4, pages 313 - 332
The Július metamorphosed manganese occurrence is situated near the Betliar village in the Spišsko-gemerské rudohorie Mts. (Western Carpathians). Mineralization occurs in the form of manganese carbonate-silicate lenticular body hosted in Lower Paleozoic metasedimentary and metavolcanoclastic rocks of the Bystrý potok Formation, Gelnica Group, Gemeric Unit. The Mn mineralization dominantly consists of rhodochrosite, pyroxmangite, spessartine, magnetite, clino-suenoite, clino-ferro-suenoite, tephroite, pyrophanite and pyrosmalite-(Mn) alongside with pyrite, pyrrhotite, galena, sphalerite, cobaltite, gersdorffite, siegenite, violarite and minor pentlandite and millerite. Very rare minerals, such as hejtmanite, bafertisite as well as a two recently approved members of the epidote supergroup (ferriandrosite-(Ce) and vielleaureite-(Ce)) were also identified. Significant feature of studied mineralization in comparison with the other occurrences of metamorphosed manganese mineralization in the Spišsko-gemerské rudohorie Mts. is the absence of rhodonite. Mineralization at the Július occurrence originates from heterogenous sediment with occurrence of manganiferous, calcareous, argillaceous and terrigenous material with quartz and Ba-rich minerals locally incorporated by material from a volcanic source. Based on mineralogy and ore textures, two metamorphic stages affecting the final mineral composition of Mn mineralization can be distinguished. Generally, the mineral assemblage was likely formed during the Variscan metamorphic stage in the p-T conditions approximately 420-450 °C and pressure 2-4 kbar, as a peak of a metamorphism can be considered the high-grade greenschist facies conditions. Alpine metamorphic phase determined the appearance of veins and veinlets composed of rhodochrosite-chamosite-quartz, pyroxmangite and spessartine. In agreement with lowering temperature of metamorphism and with higher mobility of REE, minerals such as epidotes, baryte and pyrosmalite-(Mn) were formed. Hydrothermal activity led to the formation of sulphides with slightly increased content of Mn. Final stage of metamorphic evolution was influenced by local metasomatic processes. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.384 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.384