NÁLEZ NEOBVYKLÉ MLADŠÍ SIDERITOVÉ VÝPLNĚ RUDNÍ ŽÍLY V HRABŮVCE (KULM NÍZKÉHO JESENÍKU)

A fine-grained siderite rock was found to form a younger stage of subvertical NNW-SSE trending polymetallic post-Variscan Zn-Pb vein hosted by the Lower Carboniferous greywackes in the Hrabůvka quarry. The rock is formed mainly by sparitic Fe-rich carbonate (siderite to Mg-siderite) containing small admixture (~15 wt. %) of detritic component composed of clay, and fragments of older hydrothermal minerals and host greywacke. Except of siderite, the authigenic phases are represented also by minor framboidal pyrite and sphalerite. Bulk chemical composition is characterized by high both FeO (40.6 wt. %) and CO2 (32.6 wt. %) contents. Rare earth element abundances and stable isotope data are similar to those of local Tertiary sediments and different from those characterizing the post-Variscan vein dolomite. It is concluded that the studied siderite probably originated during sideritization of carbonate-rich Tertiary sediment, which sink into the reactivated fault that has been already earlier (during the post-Variscan period) cemented by Zn-Pb mineralization

A find of dense CO2 fluid inclusion in zircon from the Quaternary fluvial gravel-sands at Hulín

High density CO2 fluid inclusion was found in one zircon crystal separated from commercial gravel-sand supplied from sand-pit at Hulín, where the Quaternary fluvial sediments are exploited. The prismatic, slightly rounded 19x10 μm large fragment of a zircon contained single elongated 6 μm long fluid inclusion which appears to be monophase at room temperature. The microthermometric measurements revealed presence of almost pure CO2 (melting temperature as low as -56.9 °C) that homogenized to liquid phase at -49.2 °C. The corresponding density for pure CO2 system is 1.152 g/cm3. Yet, fluid inclusions with similar characteristics are not known from the possible source area, from which the clastic material could have been derived. Theoretically, the dense CO2 fluids could be bound to high-grade metamorphic rocks (amphibolite facies or higher) or to low-grade metamorphic rocks in areas of low geothermal gradient.High density CO2 fluid inclusion was found in one zircon crystal separated from commercial gravel-sand supplied from sand-pit at Hulín, where the Quaternary fluvial sediments are exploited. The prismatic, slightly rounded 19x10 μm large fragment of a zircon contained single elongated 6 μm long fluid inclusion which appears to be monophase at room temperature. The microthermometric measurements revealed presence of almost pure CO2 (melting temperature as low as -56.9 °C) that homogenized to liquid phase at -49.2 °C. The corresponding density for pure CO2 system is 1.152 g/cm3. Yet, fluid inclusions with similar characteristics are not known from the possible source area, from which the clastic material could have been derived. Theoretically, the dense CO2 fluids could be bound to high-grade metamorphic rocks (amphibolite facies or higher) or to low-grade metamorphic rocks in areas of low geothermal gradient

XENOTIM-(Y) Z RUDNÍ ŽÍLY NA LOKALITĚ ZLATÝ DŮL U HLUBOČEK (KULM NÍZKÉHO JESENÍKU)

Xenotime occurs within polymetallic vein in dump material of former silver prospect at Zlatý důl near Hlubočky. The sample is formed by brecciated host Lower Carboniferous Culmian shales and siltstones, which are cemented by hydrothermal phases (quartz, siderite, carbonate of dolomite-ankerite series, chalcopyrite, dickite). Isometric grains of xenotime, up to 15 μm big, cut in form of a veinlet the hydrothermal quartz. Electron microprobe analyses showed that the studied phase is stoichiometric xenotime-(Y) containing 20 at. % of MREE and HREE instead of Y. Xenotime from Zlatý důl represents the first occurrence of MREE-HREE enriched REE-phase from hydrothermal veins in the whole Moravian-Silesian Culm. As such, its occurrence is a manifestation of (i) mobility of REE+Y under low-temperature conditions, and (ii) significant fractionation of REE in hydrothermal fluids hosted by low-grade Culmian metasediments

Kompozičně neobvyklé struskové hmoty z polykulturní archeologické lokality Boršice v podhůří Chřibů

We present results of laboratory investigation of slag-like artifacts, found on an archaeological site near Boršice, known by occurrence of artifacts from the Early Neolithic (5700–5000 BC), Bronze and Early Medieval Ages. The grey-coloured foamy slag-like artifacts reach up to 5 cm in size and often display original lava-like surface. These slags are formed especially by strongly potassic (15–23 wt. % K2O) silicic (54–72 wt. % SiO2) glass with elevated contents of Ca (4–15 wt. % CaO), P (1–5 wt. % P2O5) and Mg (1–5 wt. % MgO) and only traces of Al, Mn and Fe (below 0.14 wt. % of oxides of each of these elements). Glass phase is partly altered due to weathering, which caused the glass hydration and almost complete loss of K. Sparse minute crystals of wollastonite (CaSiO3) and an unidentified Ca-K-Si-P-O phase (with highly variable compositions and poor stoichiometry) occur in places in the glass phase. We suggest that the origin of the studied slag-like artifacts is probably connected with either modern or ancient production of glass. However, it is certainly not modern foam glass, industrially produced worldwide from used waste glass. Based on average chemical composition of glass, we suggest that the studied artifacts could originate by smelting of a mixture of quartz sand, potash, bone ash, calcitic limestone (or calcitic marble) and dolomite in weight proportions equal to 58.9, 24.6, 4.9, 3.3, and 8.3, respectively.We present results of laboratory investigation of slag-like artifacts, found on an archaeological site near Boršice, known by occurrence of artifacts from the Early Neolithic (5700–5000 BC), Bronze and Early Medieval Ages. The grey-coloured foamy slag-like artifacts reach up to 5 cm in size and often display original lava-like surface. These slags are formed especially by strongly potassic (15–23 wt. % K2O) silicic (54–72 wt. % SiO2) glass with elevated contents of Ca (4–15 wt. % CaO), P (1–5 wt. % P2O5) and Mg (1–5 wt. % MgO) and only traces of Al, Mn and Fe (below 0.14 wt. % of oxides of each of these elements). Glass phase is partly altered due to weathering, which caused the glass hydration and almost complete loss of K. Sparse minute crystals of wollastonite (CaSiO3) and an unidentified Ca-K-Si-P-O phase (with highly variable compositions and poor stoichiometry) occur in places in the glass phase. We suggest that the origin of the studied slag-like artifacts is probably connected with either modern or ancient production of glass. However, it is certainly not modern foam glass, industrially produced worldwide from used waste glass. Based on average chemical composition of glass, we suggest that the studied artifacts could originate by smelting of a mixture of quartz sand, potash, bone ash, calcitic limestone (or calcitic marble) and dolomite in weight proportions equal to 58.9, 24.6, 4.9, 3.3, and 8.3, respectively

MINERALOGIE A PODMÍNKY VZNIKU TIŠNOVSKÝCH BARYTOVÝCH ŽIL

Hydrothermal barite vein mineralization was studied at four localities in surrondings of Tišnov (20 km NW from Brno). Veins have strike NW-SE and crosscut rocks of the Moravian Svratka Dome. Veins consist predominantly of calcite and barite, less frequently of fluorite, quartz, dolomite, aragonite, hematite, goethite, chlorite. Traces of sulfides (chalcopyrite, galena, sphalerite, marcasite, tetrahedrite, bravoite and pyrite) are present, too. Homogenization temperatures of the fluid inclusions range between 45 and 125 °C. Cryometric measurements indicate Ca-Na-Cl and Na-Cl types of fluid. Salinity of the trapped solutions fluctuates very much (0-24 wt. % NaCl equiv.) dependently on evolution of mineralization. Oxygen and carbon isotopic composition of the parent fluid ranges between -3,5 and +5,5 per mil SMOW and between -6 and -10 per mil PDB, respectively. Mineralogical, geochemical, fluid inclusion and stable isotope data reveal basinal brines as parent fluid of the investigated mineralization

Bornite from hydrothermal mineralization of historical deposit of Zlatý důl near Hlubočky (Culm of the Nízký Jeseník Upland)

Secondary bornite occurs within quartz-carbonate ore vein in dump material at historical deposit of Zlatý důl near Hlubočky. This mineral was characterized using ore microscopy and electron microprobe analyses. The studied sample was formed by quartz, which occurs in the centre of the ore vein, carbonate of the dolomite-ankerite series, which formed bands on the edge of the ore vein and the unspecified beige coloured carbonate. The ore minerals were represented by primary chalcopyrite and secondary chalcocite, covellite and galena (the layer of galena grows on chalcocite on the edge of the altered chalcopyrite aggregate). The studied sample was partly weather-worn and especially carbonate of the dolomite-ankerite series was altered to iron oxyhydroxides. Bornite lamellae up to 100 × 40 μm were found along cracks of the chalcopyrite aggregate (where chalcopyrite is altered to chalcocite). Lamellar bornite occurs also in secondary chalcocite. Bornite contained only trace amount of Pb, other elements (Zn, Co, Ni, Mn, Cd, Hg, As, Ag, Bi, Sb, Se and Cl) were bellow the detection limits. Bornite is probably a secondary mineral, which was formed at the expense of chalcopyrite. Bornite from historical deposit of Zlatý důl represents the first occurrence of this mineral in the Bystřice Ore District and also in the whole Moravo-Silesian Culm.Secondary bornite occurs within quartz-carbonate ore vein in dump material at historical deposit of Zlatý důl near Hlubočky. This mineral was characterized using ore microscopy and electron microprobe analyses. The studied sample was formed by quartz, which occurs in the centre of the ore vein, carbonate of the dolomite-ankerite series, which formed bands on the edge of the ore vein and the unspecified beige coloured carbonate. The ore minerals were represented by primary chalcopyrite and secondary chalcocite, covellite and galena (the layer of galena grows on chalcocite on the edge of the altered chalcopyrite aggregate). The studied sample was partly weather-worn and especially carbonate of the dolomite-ankerite series was altered to iron oxyhydroxides. Bornite lamellae up to 100 × 40 μm were found along cracks of the chalcopyrite aggregate (where chalcopyrite is altered to chalcocite). Lamellar bornite occurs also in secondary chalcocite. Bornite contained only trace amount of Pb, other elements (Zn, Co, Ni, Mn, Cd, Hg, As, Ag, Bi, Sb, Se and Cl) were bellow the detection limits. Bornite is probably a secondary mineral, which was formed at the expense of chalcopyrite. Bornite from historical deposit of Zlatý důl represents the first occurrence of this mineral in the Bystřice Ore District and also in the whole Moravo-Silesian Culm

NÁLEZ KARBONÁTOVÉ HORNINY V LOMU U OMIC (BRNĚNSKÝ MASIV)

A carbonate rock was found in the quarry near Omice. Several small (up to 10 cm) lenses of grey „limestone“ were located within distinct fault structure. Microscopic and cathodoluminescence observations show that the rock is formed by fine-grained calcite which contains several types of larger objects (algal structures, worm borings, relics of the dolomite crystals, clasts of the surrounding crystalline rocks and next unidentified structures). Carbonate rock was affected by both ductile and brittle deformation. The rock has unusual isotopic composition (δ13C = -14.2 ‰, δ18O = -5.2 ‰ PDB). We suppose that the studied carbonate originated in limited, shallow and hypersaline? environment (lagoon, lake?). Structures, oxygen isotope composition and mineral composition were later slightly modified during diagenesis and deformation

Basic characteristics of fluids from quartz vein at Budeč (Moldanubicum)

Fluid inclusions and oxygen isotope composition have been studied in quartz sampled from a ~30 cm thick NE-SW trending anchimonomineral quartz vein hosted by Moldanubian gneisses at Budeč. Fluid inclusions contain, in addition to aqueous fluid and vapour bubble, also three types of heterogeneously trapped solids (possibly carbonate and unknown isometric and accicular phases). The vapour-containing fluid inclusions homogenized between 95 and 215 °C. Cryometric data are rather exotic: Tf = -14 to -49 °C, Te = -8 to -38 °C, Tm of an unknown phase = -0.3 to -6.4 °C, Tm ice = 0.0 to -5.2 °C. The δ18O of quartz is 0.0 ‰ SMOW, corresponding to fluid δ18O between -11 and -22 ‰ SMOW calculated for the total range of Th values. It may be concluded that the quartz originated from a rather specific fluid system. The salt content of fluids (including chlorides, and possibly also sulphates and/or bicarbonates) may have been possibly acquired due to various low-temperature dissolution, hydrolytic and/or oxidation reactions of meteoric water and silicate rocks.Fluid inclusions and oxygen isotope composition have been studied in quartz sampled from a ~30 cm thick NE-SW trending anchimonomineral quartz vein hosted by Moldanubian gneisses at Budeč. Fluid inclusions contain, in addition to aqueous fluid and vapour bubble, also three types of heterogeneously trapped solids (possibly carbonate and unknown isometric and accicular phases). The vapour-containing fluid inclusions homogenized between 95 and 215 °C. Cryometric data are rather exotic: Tf = -14 to -49 °C, Te = -8 to -38 °C, Tm of an unknown phase = -0.3 to -6.4 °C, Tm ice = 0.0 to -5.2 °C. The δ18O of quartz is 0.0 ‰ SMOW, corresponding to fluid δ18O between -11 and -22 ‰ SMOW calculated for the total range of Th values. It may be concluded that the quartz originated from a rather specific fluid system. The salt content of fluids (including chlorides, and possibly also sulphates and/or bicarbonates) may have been possibly acquired due to various low-temperature dissolution, hydrolytic and/or oxidation reactions of meteoric water and silicate rocks

Finding of the aluminum-rich spinelides and corundum in the slags produced by silver metallurgy from the Stříbrné Hory in the Havlíčkův Brod Ore District

This work deals with the unique association formed by spinelides and corundum in historical slag after smelting of silver ore from the site Stříbrné Hory in the Havlíčkův Brod Ore District. To study these phases, polarizing microscope and electron microprobe (WDX and EDX) were used. The slag consists primarily of glass and residual quartz, which also contained sillimanite needles. During smelting the quartz and sillimanite have been partially melted and aluminium-rich spinelides crystallized in the surrounding glass. Euhedral crystals of spinelides range 5 to 25 μm in size and are composed predominantly of hercynite (55–58 mol. %), to a lesser extent gahnite (21–24 mol. %), spinel (18–24 mol. %) and galaxite (4–5 mol. %). Corundum probably originated during the smelting from secondary mullite at temperatures around 1 300 °C. Corundum together with glass form a paramorphosis aft er sillimanite aggregate.This work deals with the unique association formed by spinelides and corundum in historical slag after smelting of silver ore from the site Stříbrné Hory in the Havlíčkův Brod Ore District. To study these phases, polarizing microscope and electron microprobe (WDX and EDX) were used. The slag consists primarily of glass and residual quartz, which also contained sillimanite needles. During smelting the quartz and sillimanite have been partially melted and aluminium-rich spinelides crystallized in the surrounding glass. Euhedral crystals of spinelides range 5 to 25 μm in size and are composed predominantly of hercynite (55–58 mol. %), to a lesser extent gahnite (21–24 mol. %), spinel (18–24 mol. %) and galaxite (4–5 mol. %). Corundum probably originated during the smelting from secondary mullite at temperatures around 1 300 °C. Corundum together with glass form a paramorphosis aft er sillimanite aggregate

Evidence for activity of low-temperature Ca-Na-Cl brines in feldspathitized granites of the feldspar deposit near Krásno (Krudum granite body)

The quartz-fluorite NNW–SSE trending vein mineralization hosted by alkali-feldspar syenites and leucocratic topaz-albite granites of the Vysoký Kámen stock (Krudum granite body) formed from low-salinity (0–5 wt. % NaCl eq.) and low-temperature (Th =90–132 °C) aqueous fluids. Both quartz and fluorite host secondary fluid inclusions which contain high-salinity (16–26 wt. % NaCl eq.) low-temperature (Th = 89–138 °C) Ca-Na-Cl brines. Two compositional subtypes of brines can be identified (Na-rich hosted by FI in fluorite and Ca-rich hosted by FI in quartz). The microthermometric parameters of brine-bearing fluid inclusions are fully comparable to the high-salinity fluids that participated during formation of many types of vein mineralizations during the post-Variscan period in the Bohemian Massif. The brines probably migrated along the adjacent NNW–SSE trending Vysoký Kámen fault.The quartz-fluorite NNW–SSE trending vein mineralization hosted by alkali-feldspar syenites and leucocratic topaz-albite granites of the Vysoký Kámen stock (Krudum granite body) formed from low-salinity (0–5 wt. % NaCl eq.) and low-temperature (Th =90–132 °C) aqueous fluids. Both quartz and fluorite host secondary fluid inclusions which contain high-salinity (16–26 wt. % NaCl eq.) low-temperature (Th = 89–138 °C) Ca-Na-Cl brines. Two compositional subtypes of brines can be identified (Na-rich hosted by FI in fluorite and Ca-rich hosted by FI in quartz). The microthermometric parameters of brine-bearing fluid inclusions are fully comparable to the high-salinity fluids that participated during formation of many types of vein mineralizations during the post-Variscan period in the Bohemian Massif. The brines probably migrated along the adjacent NNW–SSE trending Vysoký Kámen fault