Polymetamorfně přepracované, páskované a silicifikované magnetitové rudy v desenských rulách (Silesikum, Česká republika)
Článek v PDFPolymetamorphic overprinted and silicified banded magnetite ores from the Desná gneisses (Silesicum, Czech Republic)
Magnetite ores of the Desná Group in Silesicum represent metamorphosed and silicified banded iron ores, primarily of magmatic origin, similar to the „Itakpe“ ore type in Nigeria. Mn-rich bands consisting mainly of spessartite dominated rocks are also present in the heterogeneous ores. They are suggested to be identical to the gondites – silicate facies of iron formation (type Algoma).
The Itakpe banded iron ore deposit in Nigeria is connected with basic intrusions which were metamorphosed during the Pan African orogeny (about 580 Ma). The basic rocks are represented by gabbros with tschermakite hornblend which occur in the form of apophyses in „Basement-Cornplex“ (of Liberian age) which is composed of biotite-sillimanite gneisses (MÜCKE, NEUMANN 1986).
In the case of magnetite ores in the Desná Group the situation is similar: basic ore-rich apophyses of tholeiitic character and related to the type of Sobotín basic body penetrated the Desná gneisses. Heterogeneous ores and host rocks were subsequently affected by retrogressive Variscian metamorphism, tectonized and intensively silicified.
Arno Mücke, Mineralogisch-Petrologisches Institut, Georg-August-Universität, 37077 Göttingen, Germany e-mail: amuecke@sci.muni.cz
Zdeněk Losos, Institute of Geological Sciences, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic, e-mail: losos@sci.muni.cz