|
|
Volcanic-hosted massive sulfide deposits: structure, origin and examples from the Iberian Pyrite Belt
Krátký, Ondřej ; Dolejš, David (advisor) ; Zachariáš, Jiří (referee)
English abstract The volcanic-hosted massive sulfide deposits (VHMS) represent one of the key deposit types in the modern world. Due to their polymetallic composition (Zn, Pb, Cu, Ag, Au and Sn in some cases) they are important source of the base metals as well as the precious metals. They have been forming through the Earth's history and are actively forming even now on a modern sea- floor through emanations of hot metal-bearing fluids. Extensive study of the volcanic-hosted massive sulfide deposit began in 1960s after discovery of active seafloor vents on the bottom of the Red Sea (e.g. Miller et al., 1966) in form of black smokers. They represent channels and are results of emanation of the hydrothermal fluids into the water column and actual evidence of the hydrothermal processes. Hydrothermal fluids were enriched in various elements, including base and precious metals. Certain elements (specifically metals) were leached from the host rock (volcanic and sedimentary) by the percolating seawater. This seawater was heated and modified into hydrothermal fluid by a heat from a magmatic intrusion, which represents the driving force of the whole hydrothermal system. This intrusion can be of variable composition - from basic to felsic. Sometimes fluids that are produced by this intrusion are also enriched in...
|
|
|
Mineral assemblages and conditions of origin of metamorphic skarns in the Bohemian Massif
Bubal, Jan ; Dolejš, David (advisor) ; Pertoldová, Jaroslava (referee)
ENGLISH SUMMARY MINERAL ASSEMBLAGES AND CONDITIONS OF ORIGIN OF METAMORPHIC SKARNS IN THE BOHEMIAN MASSIF Calcic-iron skarns are a characteristic rock type of regional metamorphic complexes wirkude. In the Bohemian Massif, characteristic enrichment in Ca, Al, and Fe as well as mineral assemblages, textures are similar to their contact metamorphic counterparts but their origin remains unclear. In this thesis, we document petrography, mineral assemblages and chemistry of skarns and apply phase equilibrium models to reconstruct conditions of their formation. Skarns at Vlastějovice (Moldanubian zone), Malešov (Kutná Hora complex) and Měděnec (Saxothuringian zone) contain primary assemblage of garnet, clinopyroxene and magnetite, followed by crystallization of amphibole, epidote, formation of carbonate veins, and silicification. Some of these phenomena are related to the emplacement and fluid release from dykes of granitic pegmatites. Garnet represents the most abundant rock-forming minerals. Primary fine-grained aggregates (Gr30-50Alm30-40And10-30) are often recrystallized into euhedral grains or monomineralic masses with preserved chemical zoning (Gr05-30Alm1-30And40-90). At the Měděnec locality, garnets evolved towards andradite-skigaite composition. Clinopyroxene belongs to the diopside-hedenbergite series,...
|
guest ::
