Search

Various marbles from historic quarries of the Czech Republic were examined by means of cathodoluminescence (CL) spectroscopy (quantitative data) to determine the possible inclusion of the method in marble provenance studies. The methodology used was based on a combination of electron microprobe analysis (Ca, Mg, Fe and Mn composition) and CL spectroscopy (intensity) of calcite and dolomite grains of the marbles studied. Several statistical techniques were applied to the CL-spectra to find the most effective way of characterization of the CL-spectra for provenance discrimination. The combination of Mg-admixture of calcite and position of the maximum (i.e., centre) of a single Gaussian curve was revealed to be the most discriminative dependence of the marbles studied. [ABSTRACT FROM AUTHOR]

Titanium contents of both vein and magmatic quartz from five Bohemian gold deposits with known P-T history were used to calculate/discuss the titanium oxide activities (aTiO2) of natural quartz formed in the absence of Ti-buffering phases at 250-550 °C and 0.1-4 kbar. Data suggest significant variations in aTiO2 during vein quartz formation, due to variation of P, T and growth rate. Negative correlation between aTiO2 and quartz formation temperature was documented for intrusion-related gold deposits, implying quartz precipitation under closed-system conditions (i.e., without substantial equilibration of the ascending fluid with surrounding rocks). We propose a relationship for quantifying disequilibrium quartz formation that can be readily applied to quartz with known P-T history. The relationship was tested on natural samples exhibiting both rapid and slow crystallization. An example of extreme Ti enrichment (up to ~30 ×) in quartz, associated with its rapid growth, is described and discussed. [ABSTRACT FROM AUTHOR]

The trace-element contents in gold-bearing and barren quartz veins from eight Au, Au-Ag and Sb-Au Variscan deposits in the Bohemian Massif have been determined in situ in order to evaluate the differences between the various types of gold deposits and discuss trace-element variations in the successive generations of quartz veins. The variability of Ti, Al, Ge, Li and Sb abundances obtained by Laser-Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS) roughly correlates with the origin and the temperature of the mineralizing fluids. The Al content ranges up to 4020 ppm (median value 230 ppm), while the Li content is generally low (< 4 ppm). The elevated Sb content (30-360 ppm Sb) is only related to quartz that immediately preceded deposition of Sb-rich phases. The titanium content of the ore-bearing vein quartz follows bimodal distribution: gold deposits with assumed higher temperature (> 450 °C) formation exhibit higher median values (~10 ppm Ti) than medium-to-low (< 300 °C) temperature deposits (~2 ppm Ti). A statistically significant threshold value (8 ppm Ti) has been recognized as an empirical tool for discriminating between them. In terms of the Ti and Al contents, the studied Bohemian gold deposits fall within and in between fields of orogenic gold and porphyry deposit types. [ABSTRACT FROM AUTHOR]

The Giftkies mine is the only known locality of rutherfordine within the Jáchymov ore district s.l., which is famous for the occurrence of many uranyl carbonates. Uranyl monocarbonate rutherfordine, UO2(CO3), investigated in this study, has been found in significant amounts in the abandoned arsenic mine at Giftkies site (Jáchymov, Czech Republic), together with other uranyl carbonates, common liebigite and scarce agricolaite. The possible specific conditions of rutherfordine formation prompted the detailed study with the following analytical methods. XRD methods helped identify above mentioned minerals as well as other secondary minerals reported from this site, 31 minerals in total. The mineralization sequence was investigated and determined by both optical and scanning electron microscopy to be: quartz → early siderite → late siderite → pyrite → iron oxyhydroxides → rutherfordine. This microscale investigation of textural features and element admixtures helped to create above mentioned paragenetic scheme. Further on alpha spectrometry and radiometric dating of rutherfordine helped to build a timeframe. A daughter deficiency method using 230Th/234U isotopic pair provides late Holocene ages and suggests at least two rutherfordine formation episodes (4600--2600 years BP and 1350--300 years BP respectively). According to data, we claim that supergene processes that lead to rutherfordine crystallization at the site started at the beginning of the Subboreal period and lasted until nowadays. [ABSTRACT FROM AUTHOR]

The Krásná Hora-Milešov and Příčovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks. Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krásná Hora-Milešov) or are associated with local strike-slip faults (Příčovy). Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at ~250 to ~130 °C and gold at ~200 to ~130 °C from low-salinity aqueous fluids. The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 °C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature (~250 MPa, ~400 °C). The estimated oxygen isotope composition of the ore-bearing fluid (4 ± 1‰ SMOW; based on post-ore calcite) suggests its metamorphic or mixed magmatic-metamorphic origin and excludes the involvement of meteoric water. Rapid cooling of warm hydrothermal fluids reacting with 'cold' host rock was probably the most important factor in the formation of both stibnite and gold. [ABSTRACT FROM AUTHOR]

We present Pb-isotope composition of parent granite and 25 samples of low-temperature mineral assemblages filling open fractures in a granite from southern part of the Melechov Massif of the Moldanubian Batholith, sampled over the 100 m deep borehole PDM-1. The fillings have usually higher U/Pb and 206Pb/207Pb ratios compared to the host granite, which mostly enables dating by one-stage model (i.e., determination of time when their isotopic composition was within the range of the host rock). The most abundant group (12 samples) yielded maximum model ages between 150 and 225 Ma, while their minimum model ages range from 0 to 145 Ma. Variscan ages of up to 300 Ma are probable in the case of 4 samples. Three samples with the highest U/Pb ratios yielded Tertiary model ages (maximum 30-60 Ma); two of them are chemically very contrasting (mainly rich in Mn oxides). It follows that joints could experience several events of uranium and/or lead redistribution throughout their late-Variscan and post-Variscan evolution, with little importance of Quaternary processes. [ABSTRACT FROM AUTHOR]

he Ševětín Pluton, located c. 15 km NNE of České Budějovice, is a small, isolated, petrologically and structurally complex intrusive body that is genetically related to the youngest intrusions of the Moldanubian Batholith. As documented in this study, its overall shape, internal magmatic fabric as well as brittle structures (dikes, veins, joints, faults) are, however, related to the formation and polyphase tectonic evolution of the Blanice Graben, an about 200 km long and 5-15 km wide NNE-SSW-trending, deep-seated fault zone that cuts across the Moldanubian Unit. In total, one pre-intrusive and three syn- to post-intrusive tectonic phases have been distinguished. The oblique, NW-SE oriented compression controlled both the intrusion of the Ševětín biotite-muscovite granite and the early stage of its brittle deformation. Sigmoidal pattern of magnetic foliations in this pluton documents its mostly solid-state deformation during oblique sinistral movements on the main faults of the Blanice Graben. The subsequent strike-slip phase was characterized by E-W oriented subhorizontal extension and can be correlated with the intrusion of c. 270 Ma old microgranodiorite dikes. The last extensional phase was associated with the formation of subeconomic Pb-Zn-(Ag?) quartz-calcite veins at c. 265 Ma. [ABSTRACT FROM AUTHOR]

The stratiform deposit of mercury at Horní Luby near Cheb (Czech Republic) is hosted by Ordovician phyllites of Vogtland-Saxony Paleozoic Unit in the Saxothuringian Zone of the Bohemian Massif. Ore is represented by cinnabar disseminated within the phyllite and by lenticular bodies rich in massive cinnabar (lenses with a thickness of up to 1 m and length along the strike varying from less than 1 m up to 20 m). Cinnabar is accompanied by pyrite and locally also siderite. The P-T history of the mineralization was deciphered by the study of fluid inclusions. Early fluids are represented by a homogenous H2O-CO2, fluid trapped in secretion quartz. This fluid underwent several heterogenization events starting from approximately 300 °C and continued down to 200-150 °C. Metamorphic quartz of secretion origin crystallized at -300 °C, while hydrothermal pyrite crystallized at 220-210°C and cinnabar at 195-160 °C. The formation of the richest ore was associated with the replacement of metamorphic quartz in phyllites by the cinnabar in weakly alkaline solutions. The cinnabar is pure phase, free of admixtures (Bi, Sb, Zn, Fe, and Cu). It is accompanied by minute blebs of Hg-bearing sphalerite (11-12 wt. % Hg) that might indicate earlier presence of the zincian metacinnabar and more complex metamorphic history of the ore. The primary source of mercury is thought to be Lower Paleozoic submarine volcanism. The formation of ore bodies is, however, associated with metamorphic mobilization of mercury during the late stages of the Variscan orogeny. Despite being relatively small, the mercury deposit at Horní Luby competed with the mines in Idrija (Slovenia) and Almadén (Spain) in the 16th century. The production of mercury at Horní Luby is estimated to have corresponded to c. 10-30 % of the mercury production in the mines of Idrija and Almadén at that time. In addition to Venice, the mercury from Horní Luby was also supplied to Niirnberg, Antwerp and Lyon. In 1520-1540, the production of mercury from the Horní Luby mines was 6 to 15 tons per annum. The mines were abandoned in 1597. Attempts to reinstitute mining activity in the 17th, 18th and 19th centuries were not very extensive and always failed. The total production of the Horní Luby mines during the whole mining history is estimated to have been at least 200 tons of mercury. Much of this amount was extracted between 1520 and 1540, with a minor portion between 1560-1570. [ABSTRACT FROM AUTHOR]

The Jílové deposit in the central part of the Bohemian Massif represents a vein to stockwork type of orogenic-type gold deposit. It is hosted by Neoproterozoic rocks of the Jílové Belt and by various magmatic dikes related to the ~355 to ~335Ma Central Bohemian Plutonic Complex. The deposit is situated along the terrane boundary of the Teplá Barrandian and Moldanubian units. The deposit offered an exceptional opportunity to trace O, C, S and Sr stable isotope evolution of parent fluids based on combined mineralogical and geochemical study of carbonate, quartz, scheelite, and sulfide minerals, which represent six stages of mineralization, including the gold-bearing event. Stable isotope data and mineral and isotope thermometry indicate gangue and ore mineral formation between ~350°C and <100°C, which can be divided into 6 stages. Scheelite-bearing assemblages (stages 2–3) precipitated at 292±8°C from a fluid with calculated values: δ18OSMOW =+4.2±0.5‰ and δ13CPDB =−11±1‰. Gold precipitation (stage 5) probably started at about 300°C, but the major event probably occurred at 230±30°C from a fluid with more variable isotope values (δ18OSMOW =+2.5 to +5‰ and δ13CPDB =−9 to −13.5‰). The carbon speciation was characterized by predomination of dissolved CO2 (H2CO3ap.) in the fluids. Some gold, however, undoubtedly precipitated from bicarbonate dominated fluids even at <120°C. Extreme variations in the δ18O values of carbonate minerals, obtained from sampling profiles across individual veins with macroscopic gold, revealed severe thermal gradients during vein formation (~50 to ~100°C difference of crystallization temperatures between the vein margin and core). The sulfur stable isotope composition of sulfide minerals indicates the dominant role of sulfur remobilization from Neoproterozoic rocks and stratiform mineralizations of the Jílové Belt by Variscan hydrothermal fluids. Similarly, the Sr-isotope composition of carbonates indicates both relatively primitive (87Sr/86Sr=0.7055) and more evolved (87Sr/86Sr~0.7090) fluid compositions, probably indicating fluid exchange with the Jílové Belt and the Central Bohemian Plutonic Complex rocks, respectively. Age determination of hydrothermal muscovite (related to stage 2) via 40Ar/39Ar indicated an age of 339.0±1.5Ma for the quartz veins. The mineralization is essentially coeval with the late intrusive phases of the Central Bohemian Plutonic Complex (i.e. the ultrapotassic suite) and with late-orogenic large-scale tectonic movements at the boundary between the two crustal terranes (Teplá-Barrandian and Moldanubian). Based on evaluation of the available age data on the hydrothermal and magmatic activity within the broader area of the Central Bohemian Plutonic Complex, we suggest two intervals of gold mineralization: 347 to 341Ma and 340 to 337Ma. The former interval overlaps with the intrusive activity of the Blatná high-K suite (granodiorite). The associated gold deposits (Mokrsko and Petráčkova hora) exhibit strong affiliation to the intrusion-related-gold-type deposit. The later interval overlaps with the ultrapotassic magmatism and is associated with more or less “classical” orogenic-gold-type deposits (Jílové, Bělčice, Libčice deposits). [ABSTRACT FROM AUTHOR]

The Roudný gold deposit, hosted by a large-scale NNE-SSW trending fault zone (the Blanice Graben), represents a type locality of low-fineness gold (Au-Ag) mineralization in the Bohemian Massif. In order to decipher its structural evolution, we performed a detailed analysis of brittle to brittle-ductile structures on outcrops and of structures described in unpublished historical materials. Three stress phases were distinguished: compressional, strike-slip, and extensional. Most hydrothermal veins originated during the strike-slip and extensional phases. Based on a comparison with the nearby Ratibořské Hory-Stará Vožice deposit, a representative of Ag-Pb-Zn vein type mineralization in the Blanice Graben, we conclude that the structural pattern of both ore deposits/mineralizations (Ag-Pb-Zn and Au-Ag) is compatible with the overall sinistral strike-slip evolution of the Blanice Graben (c. 280-270 Ma). Whereas most of the Ag-Pb-Zn veins represent typical extension veins/fractures, early gold-bearing quartz veins of the Roudný, deposit were probably initiated as Riedel R' shears and were later reopened during the extensional phase. [ABSTRACT FROM AUTHOR]

Gold-bearing quartz veins of the Bělčice ore district are hosted by I-type Variscan Blatná granodiorite of the Central Bohemian Plutonic Complex. The quartz gangue precipitated from aqueous-carbonic fluids (3-7 wt. % NaCl eq.) with significant methane admixture (up to 15 mol. % of CH4) at c. 350-400°C and 200-400 MPa. The ore stage including gold precipitation occurred at lower temperatures (300 to 250 °C) and pressures (∼ 100 MPa) from aqueous fluids. The isotope composition of the quartz and carbonate gangue indicates progressively heavier oxygen of the parental fluid (δ18Ofluid from ∼9-10 ‰ to 10-14 ‰ SMOW). This suggests ingress of metamorphic fluids equilibrated with metasedimentary country rocks into an environment dominated by I-type granitoids. Invasion of external metamorphic fluids is also supported by nearly isothermal mixing trends in aqueous fluids as documented by salinity variations (from 5.5 to 0 wt. % NaCl eq.). [ABSTRACT FROM AUTHOR]

Mineralized zones of the Variscan (348-344 Ma) Petráëkova hora gold deposit locally exhibit high-temperature (~600 to -~500 °C) hydrothermal alterations: K-alteration-I (selectively pervasive) and K-alteration-2 (fracture-related) in the granodiorite and granodiorite porphyries, and silicification- I and -2 in the country rocks (biotite hornfels and feldspathic quartzite). Alteration processes led to partial recrystallization ofprimary magmatic silicates, and to crystallization of new hydrothermal phases (K-feldspar, biotite and hornblende). Electron microprobe analyses were used to trace magmatic to hydrothermal evolution of the mineral chemistry. The K-feldspar phenocrysts in the granodiorite and granodiorite porphyry exhibit complex magmatic crystallization and resorption textures. Compositionally, K-feldspars differ especially in the barium admixture. It decreases from early (5-0.8 % celsian or 2.6-0.4 wt. % BaO; phenocrysts) to late magmatic (1.1-0% celsian; groundmass) and hydrothermal (1.2-0 % celsian) K-feldspars. No significant differences were found between the chemistry of magmatic and early hydrothermal amphiboles. They all correspond to magnesiohornblende or actinolite. Tetrahedral silica (SiIV) ranges from 6.7 to 7.8 atoms per formula unit, however; values greater than 7.2 are the most common. They exhibit positive SiIV-Mg/(Mg + Fe2+) correlation. Late hydrothermal amphibole associated with silicification-2 is also magnesiohornblende; however, it exhibits negative SiIVMg/(Mg + Fe2+) trend. Differences in the biotite composition are less pronounced in comparison to amphiboles and comprise especially a decrease in the Ti content and an increase in the Mg/(Mg + Fe2+) ratio from the magmatic to the hydrothermal biotites. Some of the fine-grained biotite aggregates (recrystallized magmatic or hydrothermal biotite) are depleted in potassium, probably due to alteration demonstrated by the presence of submicroscopic intergrowths with clay/chlorite minerals (unrecognizable in back-scattered electron mode). Broad similarities in the chemistry of magmatic and early hydrothermal silicate minerals support the high-temperature nature of the early hydrothermal stage, and point to probable admixture of exsolved magmatic fluid phase in the early hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Primary fluid inclusion in quartz crystals from barren subvertical quartz veins that crosscut the Upper Carboniferous (Upper Asturian) coarse-grained clastics at Butov near Stíbro were found to have almost the same microthermometric characteristics (salinity, temperature of homogenization and variability of filling) as fluid inclusions from mineralized veins of the Stíbro Ag-Pb-Zn ore district. The mineralization at Stříbro should be therefore Upper Asturian in age, or younger. It is notably, that fluid salinities and temperatures of veins from Butov, and also of the Stříbro district, are very similar to that of Triasic to Jurasic fluorite-barite mineralization from the Erzgebirge Mts. (Moldava, Vrchoslav deposits). [ABSTRACT FROM AUTHOR]

The Padrť Stock is a small (~5 km²) intrusion located near the SE margin of the Teplá-Barrandian Unit, Bohemian Massif, several kilometers away from the NW periphery of the Central Bohemian Plutonic Complex. On outcrops, which are all located close to the contact of the stock with Neoproterozoic sedimentary rocks, two types of granitoids were detected, fine- to medium-grained hornblende-biotite Padrť granodiorite, and, along its SW margin, fine- to medium-grained partly porphyritic biotite Teslíny leucogranite. The U-Pb zircon dating of the more voluminous Padrť granodiorite by laser ablation ICP-MS yielded a magmatic age of 342.8 ± 1.1 Ma, which is slightly lower than are the published age data for the nearby Blatná suite granitoids of the plutonic complex. The Re-Os dating of molybdenite occurring in quartz veins within a quartzite lens in close exocontact yielded ages of 337.2 ± 2.4 Ma and 339.8 ± 2.5 Ma (two samples). The data indicate that the formation of molybdenite postdated that of the magmatic rock. This is in agreement with relatively low-temperature deposition of quartz related to formation of the molybdenite, as indicated by the fluid inclusions (280 to 300 °C). [ABSTRACT FROM AUTHOR]