scholarly journals Minerály kontaminovaných granitových pegmatitů z lomu Pohled u Havlíčkova Brodu (moldanubikum), část I: oxidy, karbonáty, silikáty a fosfáty

2020 ◽  
Vol 28 (1) ◽  
pp. 132-151 ◽  
Author(s):  
Zdeněk Dolníček ◽  
Karel Malý ◽  
Jana Ulmanová ◽  
Jaroslav Havlíček ◽  
Luboš Vrtiška
Keyword(s):  
Czech Republic ◽  
Mineral Composition ◽  
Bohemian Massif ◽  
Small Body ◽  
Coarse Grained ◽  
Metamorphic Rocks ◽  
Granitic Pegmatites ◽  
Ore Minerals ◽  
Magmatic Stage

In the Pohled quarry near Havlíčkův Brod town (central part of Czech Republic), granitic pegmatites form dikes or irregular bodies cementing breccia of host metamorphic rocks (paragneisses, amphibolites) belonging to the Monotonous (Ostrong) Group of the Moldanubicum of the Bohemian Massif. Pegmatites exhibit coarse-grained textures and very simple mineral composition, which, however, was in places strongly modified by superimposed hydrothermal alterations and locally also by crystallization of ore minerals. K-feldspar, plagioclase (An0-38), biotite (phlogopite), apatite (fluorapatite to hydroxylapatite), zircon, allanite-(Ce) and part of quartz undoubtedly originated during magmatic stage. Products of hydrothermal alterations include younger quartz, Fe-Mg chlorites (older clinochlore and younger chamosite with an admixture of Ca-smectite), prehnite, clinozoisite, amphibole (actinolite), titanite, calcite, and very probably also ilmenite (with up to 22.5 mol. % of pyrophanite), rutile, anatase and V-Cr-Fe-rich grossular with 13 - 25 mol.% of goldmanite and 12 - 24 mol.% uvarovite. The elevated contents of Mg, Ca, V and Cr found in some minerals are associated with a material contamination by the surrounding metamorphic rocks (especially amphibolites, serpentinites and perhaps also graphitic lithologies), which took place with varying intensity during both magmatic and hydrothermal stages of evolution of the studied pegmatites. Geochemically, they are poorly fractionated pegmatites, whose origin was probably connected with anatexis of the host Moldanubian metamorphic rocks, which was likely associated with emplacement of adjacent small body of the Pohled Granodiorite.

Compositional and Textural Variations of Columbite-Group Minerals from Beryl-Columbite Pegmatites in the Maršíkov District, Bohemian Massif, Czech Republic: Magmatic versus Hydrothermal Evolution

2020 ◽  
Author(s):  
Štěpán Chládek ◽  
Pavel Uher ◽  
Milan Novák
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
High Mobility ◽  
Oscillatory Zoning ◽  
Hydrothermal Conditions ◽  
Magmatic Stage ◽  
Compositional Variations ◽  
Host Rocks ◽  
Crystal Volume ◽  
Residual Melt

Abstract We studied compositional variations in columbite group minerals (CGM) from several granitic pegmatites of the beryl-columbite subtype in the Maršíkov district, Silesian Domain of the Bohemian Massif, Czech Republic. The CGM are characterized by distinct zoned patterns in BSE images. Primary magmatic homogeneous to oscillatory zoning is preserved in corroded crystal cores, whereas the majority of the crystal volume is replaced by secondary complexly zoned domains formed via post-magmatic processes. The primary domains show relatively uniform evolutionary trends from core to rim, generally with steeply increasing Ta/(Ta + Nb) and negligible to slightly increasing Mn/(Mn + Fe). In contrast, the compositions of secondary CGM domains indicate a reversed evolution, with: (1) steeply decreasing Ta/(Ta + Nb) and relatively constant Mn/(Mn + Fe) characteristics for CGM in the Bienergraben and Scheibengraben pegmatites, and (2) insignificantly decreasing Ta/(Ta + Nb) and strongly decreasing Mn/(Mn + Fe) characteristics for CGM in the Schinderhübel I and Lysá Hora pegmatites. Patchy zoning and secondary evolution in CGM result from metasomatic replacement processes related to fluids. These fluids are probably late-magmatic and exsolved from the residual melt and in later stages locally mixed with external Mg-enriched fluids derived from the host rocks. The presence of volatiles (mainly H2O, F) facilitated high mobility of the elements and replacement of the early CGM. Textural characteristics and compositional variations in CGM show the complex evolution of the pegmatite system from the magmatic stage to subsolidus-hydrothermal conditions.

scholarly journals Fosfohedyfán z opuštěného železnorudného ložiska Hraničná (Slezsko, Česká republika)

2020 ◽  
Vol 28 (1) ◽  
pp. 44-47
Author(s):  
Jakub Jirásek ◽  
Dalibor Matýsek ◽  
Aneta Minaříková
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Chemical Formula ◽  
Charge Balance ◽  
Skarn Deposit ◽  
Crystalline Complex ◽  
The Czech Republic

Abandoned iron skarn deposit Hraničná is located 16 km NW of Jeseník, Silesia, Czech Republic. It is situated in the Staré Město Crystalline Complex, belt of high grade metamorphic rocks, which suppose to be a meta-ophiolite of the initial Cambro-Ordovican rifting. The deposit itself is formed by two stratiform magnetite-hematite bands within the marbles and quartz-rich biotite gneisses. Marbles containing silicates are rich in Zn and Pb and give evidence for sedimentary of volcanosedimentary origin of the ore accumulation. We collected several samples at the adit and +20 m levels of the mine which yielded phosphohedyphane. Mineral forms irregular aggregates up to 100 μm within the calcite-dolomite-magnetite skarn. Its average chemical formula from 7 WDS spots is (Ca2.07Sr0.03Ba0.01Mg0.02Pb3.23Zn0.01Fe0.09Al0.01)Σ5.47[(PO4)2.53(AsO4)0.03(SO3)0.01(SiO4)0.24]Σ2.81[Cl1.05F0.20]Σ1.25 based on 13 O+Cl+F. Use of the normalization to Ca1 + Ca2 = 5 and employing the charge balance could lead to the possible presence of (CO3)2- up to 0.60 apfu, resp. 3.61 hm. % CO2; this possible content do not have any effect on mineral classification. It is, therefore, fifth reported occurrence of this mineral in the territory of the Czech Republic and the Bohemian Massif.

Secondary Beryl in Cordierite/Sekaninaite Pseudomorphs from Granitic Pegmatites – A Monitor of Elevated Content of Beryllium in the Precursor

2020 ◽  
Author(s):  
Petr Gadas ◽  
Milan Novák ◽  
Michaela Vašinová Galiová ◽  
Adam Szuszkiewicz ◽  
Adam Pieczka ◽  
...  
Keyword(s):  
Czech Republic ◽  
Chemical Composition ◽  
Limit Of Detection ◽  
Coarse Grained ◽  
Secondary Minerals ◽  
Moldanubian Zone ◽  
Granitic Pegmatites ◽  
Icp Ms ◽  
Mineral Assemblages ◽  
Host Rocks

Abstract Cordierite-group minerals (cordierite and sekaninaite) from granitic pegmatites are often strongly to completely altered to a fine- or coarse-grained mixture of muscovite, chlorite and/or, biotite, along with several less common secondary minerals, including mainly paragonite, tourmaline, and secondary beryl. The mixture is a common product of early subsolidus hydrothermal alteration at the examined pegmatites of the beryl-columbite subtype – Věžná I and Drahonín (Moldanubian Zone, Czech Republic) and Mount Begbie (Shuswap Complex, Canada); of the beryl-columbite-phosphate subtype – Szklary (Góry Sowie Block, Poland); and of miarolitic intragranitic pegmatites – Zimnik (Massif Strzegom-Sobótka, Poland). We studied in detail (EPMA, LA-ICP-MS) relics of primary cordierite/sekaninaite: Věžná I (Crd77–72Sek27–22MnCrd2–1, Be = 0.39–0.25 apfu, Li = 0.06–0.04 apfu), Drahonín (Crd13–9Sek74–71MnCrd17–16, Be = 0.24–0.18 apfu, Li = 0.07–0.05 apfu), Szklary (Crd50–49Sek30–26MnCrd25–21, Be = 0.45–0.41 apfu, Li ≤ 0.02 apfu), Mount Begbie (Crd34–33Sek53–43MnCrd24–14, Be = 0.33–0.29 apfu, Li = 0.26–0.23 apfu), and Zimnik (Crd2–1Sek75–71MnCrd28–23, Be = 0.25–0.15 apfu, Li = 0.18–0.12 apfu). Secondary beryl has a similar Mg/(Mg+Fe) ratio to its cordierite/sekaninaite precursor but is Mn depleted. The mineral assemblages and textures of the pseudomorphs were examined with a focus on secondary beryl, which forms anhedral grains to subhedral elongated crystals, up to 0.3 mm in size, or aggregates of these in textural equilibrium with associated phyllosilicates and tourmaline. Tourmaline is known from Věžná I, Drahonín, Mount Begbie, and Zimnik, the last also with topaz and “zinnwaldite” (a mineral with chemical composition between siderophyllite and polylithionite). Secondary beryl in pseudomorphs after cordierite/sekaninaite from granitic pegmatites and more evolved granites may have been often overlooked; hence, we present its textures and morphology so that it can be recognized during routine EPMA study and to study the source of elevated concentrations of Be in primary cordierite/sekaninaite. The empirical limit of detection of secondary beryl in pseudomorphs is ∼500–1000 ppm Be, which corresponds to ∼1–2 vol.% of secondary beryl. The chemical composition of the secondary beryl and other minerals indicate that the fluids responsible for the alteration were exsolved from the residual pegmatite melt and were not contaminated by fluids from the host rocks.

The earliest ostracods from the Ordovician of the Prague Basin, Czech Republic

2014 ◽  
Vol 64 (4) ◽  
pp. 367-392 ◽  
Author(s):  
Karolína Lajblová ◽  
Petr Kraft
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
Massif Central ◽  
Central European ◽  
Middle Ordovician ◽  
Prague Basin ◽  
Barrandian Area ◽  
Fossil Assemblages ◽  
European Variscides

Abstract The earliest ostracods from the Bohemian Massif (Central European Variscides) have been recorded from the Middle Ordovician of the Prague Basin (Barrandian area), in the upper Klabava Formation, and became an abundant component of fossil assemblages in the overlying Šarka Formation. Both early ostracod associations consist of eight species in total, representing mainly eridostracans, palaeocopids, and binodicopids. The revision, description, or redescription of all species and their distribution in the basin is provided. Their diversification patterns and palaeogeographical relationships to ostracod assemblages from other regions are discussed.

Mollusc successions reveal northward postglacial shifts of Alpine species ranges (Bohemian Massif, Czech Republic)

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Lucie Juřičková ◽  
Jakub Menšík ◽  
Jitka Horáčková ◽  
Vojen Ložek
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
Late Glacial ◽  
Glacial Refugia ◽  
Land Snails ◽  
Glacial Refugium ◽  
Local Climate ◽  
The Alps ◽  
Species Groups ◽  
Late Glacial And Holocene

The Alps are an important hotspot of species diversity and endemism, as well as a presumed glacial refugium of several species’ groups including land snails. The recent ranges of Alpine endemics are well known, but their fluctuations during the postglacial period mirroring local climate changes are understudied. By analysing five Late Glacial and Holocene mollusc successions from two areas in the southernmost part of the Bohemian Massif (Czech Republic) situated about 100 km north of the Alps, we reveal details of these fluctuations. The Alpine endemic rocky dweller Chilostoma achates had reached the southern part of the Bohemian Massif already in the Late Glacial and disappeared in the Mid-Holocene canopy forest optimum. On the contrary, the northern boundaries of Alpine canopy forest epigeic snails extended further north than today at the turn of the Middle and Late-Holocene, pointing to a more favourable forest microclimate. The earliest known occurrences of several temperate canopy forest central European species, especially Causa holosericea and Discus perspectivus, imply the role of different areas in the Alps as their glacial refugia.

Petrogenesis of Cenozoic high-Mg (picritic) volcanic rocks in the České středohoří Mts. (Bohemian Massif, Czech Republic)

2021 ◽  
Author(s):  
Lukáš Krmíček ◽  
Jaromír Ulrych ◽  
Emil Jelínek ◽  
Roman Skála ◽  
Simona Krmíčková ◽  
...  
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
Volcanic Rocks
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