Geologické výzkumy (na Moravě a ve Slezsku)

Corkit z ložiska Zlaté Hory-Východ

Tomáš Pek — 2024-11-11

Corkite, a Pb-Fe dominant member of the alunite supergroup, was found in the oxidation zone of the stratiform base metal deposit Zlaté Hory-Východ (Silesia, Czech Republic). It forms yellow-green coatings composed of microscopic botryoidal and globular aggregates in association with anglesite, cerusite, roentgenamorphic Mn-Pb oxides and plumbojarosite (which forms the cores of corkite aggregates but also occurs separatelly as cinnamon-brown coatings composed of microscopic rhomboedric crystals) in the cavities of quartz-limonite material. These aggregates are in polished section strongly zonal with a core made up of plumbojarosite with approx. 14 mol. % of (PO₄)^3- anion at structural position T and the peripheral parts made up of corkite. The chemical composition of corkite, determined by WDX microanalyses, is in relativelly good agreement with its theoretical formula, the anion sites are equally occupied by (SO₄)^2- and (PO₄)^3- groups or (SO₄)^2- slightly predominates. The arsenate anion is present only in trace amounts (below 0,01 apfu) which corresponds to the practical absence of As minerals in the primary ores of Zlaté Hory ore district. Problematic is the presence of silicium in all analyses which could be attributed either to anisomineral admixture or to the presence of (SiO₄)^4- at the anionic site of corkite structure. Analyses recalculated on the basis of two anion groups show excess of cations at both cation sites which could be due to the presence of unanalysed components at the anion site (probably (CO₃)^2- group. Structural position D is occupied virtually only by Pb with only subordinate amount of K. Substitution of Fe by Al at G site is very limited, Al together with Cu and Zn content is only minor. X-ray powder diffraction patterns (major lines 3.060 Å (100); 5.918 Å (75); 2.250 Å (47); 2.528 Å (34)) and calculated unit cell parameters of studied corkite are in good agreement with published data (Giuseppetti and Tadini 1987; Sato et al. 2009).

Listvenit s výskytem minerálu gersdorffit-kobaltinové řady v lomu Dřínová u Tišnova (Morava)

Pavla Hršelová — 2024-11-11

Chromian illite-magnesite-dolomite-quartz rock (listvenite-like) containing Ni-Co mineralization was found in the Svratka orthogneisses from the Dřínová quarry. The main rock-forming minerals are Fe-rich magnesite, Fe-rich dolomite, Cr-illite and quartz, less frequently calcite. Accessory minerals include chromite (with 0.841–0.886 apfu Fe²⁺ and 1.642–1.742 apfu Cr), gersdorffite-cobaltite (Ni_0.45-0.92Fe_0.01-0.34Co_0.01-0.34As_0.83-1.02Sb_0.00-0.03S₁), sulfides (pyrite, sphalerite), and apatite. The illite from the Dřínová quarry contains up to 3 wt. % of Cr₂O₃. Presence of the Cr-illite, accesory chromite, and Ni-Co sulfoarsenides represents origin from ultrabasic protolith, reflecting transformation to phyllosilicatecarbonate-
quartz listvenite.

Revize paleontologických nálezů z lokality Úsobrno

Taťána Fidlerová — 2024-11-11

The Úsobrno locality is known on the basis of fossil fauna findings, which were documented and published by Vašíček (1941). Field research has not been able to find the original locality yet. In this reason paleontological material which is deposited in the collections of ÚGV PřF MU was researched. We identified a total of 573 species which belonged mainly to the classes Gastropoda, Bivalvia, Anthozoa and Scaphopoda and compared with the original findings mentioned by Vašíček (1941). The age of the samples was determined to be the Lower Badenian.
Based on the findings, especially hermatypal corals, it can be assumed that the sea was warm (above 20 °C), well oxygenated with a soft and hard bottom and mostly shallow. Some findings of fauna from deeper marine areas (Ranella fragment, ahermatypal corals) indicate mixing or postmortem transport during sedimentation.