Karel Žák's research while affiliated with Academy of Sciences of the Czech Republic and other places

Publications (77)

Extremely low and variable concentrations of osmium (Os) and other highly siderophile elements (HSE) in most tektites make it challenging to establish direct links between these impact-related materials and their possible extraterrestrial contribution. New Os concentrations (2–43 ppt) and ¹⁸⁷ Os/ ¹⁸⁸ Os ratios (0.131–0.68) in a suite of fifteen well-characterized Australasian tektites from Laos (Muong Nong and splash-form types) with variable Ni enrichment indicate a maximum of ∼0.005% addition of a chondritic impactor. This is similar to some Australasian tektites from Vietnam with similarly low siderophile contents, but significantly lower than found in previous studies of more Ni-rich Australasian splash-form tektites and microtektites from different parts of the Australasian strewn field (e.g., Indonesia, South China Sea). The contents of HSE and Re–Os isotopic compositions of layered Muong Nong-type Australasian tektites are highly variable, suggesting mingling of crustal-derived (siderophile element-poor) and extraterrestrial (siderophile element-rich) materials. The absence of a direct correlation between HSE and Ni contents is interpreted to result from a fractionation process related to their different vaporization/condensation temperatures. The low Os abundance in most of the analyzed Australasian tektites, combined with non-radiogenic ¹⁸⁷ Os/ ¹⁸⁸ Os far below average upper continental crust, may provide a direct test to distinguish continental versus seawater impact scenario. In the absence of any specific low-Os target, a particular process of Os loss following impact is required. We envisage a scenario where evaporative loss of >>90% Os in the form of Os oxides from the overheated tektite melt is aided by volatile species derived from dissociated seawater and/or saline pore water embedded in sediments off-shore Indochina, consistent with elevated contents of halogens in Australasian tektites. This water-assisted Os loss could also play significant role for Central European tektites, while the continental surface with limited amount of water would prevent from more efficient HSE loss as could be the case for Ivory Coast tektites.
Major and trace element analyses and triple oxygen isotope measurements were performed on 11 individual specimens of Australasian tektites (AAT) with exactly known field positions from Laos. The sample set was dominated by Muong Nong‐type tektites (MNAAT), including separated layers of glass of different appearance and chemistry from four samples. This first larger set of oxygen isotope data of MNAAT revealed the δ18O range 8.7 ≤ δ18O ≤ 11.6‰ on VSMOW2 scale (12 analyses), only slightly wider than the previously reported range for splash‐form AAT. The Δ’17O values of MNAAT (−0.098 ≤ Δ’17O ≤ −0.069‰; 12 analyses) and splash‐form AAT (−0.080 ≤ Δ’17O ≤ −0.068‰; three analyses) are all in the range of data typical for terrestrial crustal rocks, with no mass‐independent oxygen isotope fractionation (from impactor or from exchange with atmospheric O2) being observed.
The Kašperské Hory deposit represents one of the economically most important hydrothermal gold deposits in the Bohemian Massif (Czech Republic). We present new Re–Os age determinations for sulfides complemented by Ar–Ar determinations on silicate minerals in order to provide temporal constraints on the deposit formation. Arsenopyrite and molybdenite formed during gold-bearing stages I–III yielded similar Re–Os ages between ~ 341 and 333 Ma, overlapping with the Ar–Ar cooling age of the metamorphic host rocks below ~ 500 °C. Continuous cooling of the ore system below 270 °C during stage III is reflected by Ar–Ar muscovite ages spanning from ~ 332 to 325 Ma representing the long interval of formation of gold-productive stage III. Thus, the Kašperské Hory gold deposit is younger than the gold deposits spatially associated with the Central Bohemian Plutonic Complex (~ 349–339 Ma) belonging to the Central Bohemian Metallogenetic Zone (e.g., Mokrsko-West, Jílové, Petráčkova Hora). This may indicate a rather close relationship to the nearby Moldanubian Batholith while still suggesting an intimate link between mineralization and Variscan orogenesis and associated magmatism.
A new locality of coarse-grained cryogenic cave carbonates has been found in the Za Hájovnou Cave in Javoříčko Karst in Central Moravia, Czech Republic. Crystals and crystal aggregates, usually up to 15 mm in size, form typical loose accumula-tions on the surface of large fallen limestone blocks and clays covering the bottoms of several cave chambers distant from the cave entrance. The cryogenic origin of the carbonates is supported by their mode of occurrence, specific crystal and ag-gregate morphology, and C and O stable isotope data. U-series dating of one sample of cryogenic carbonate (age 29.5 ±0.1 ka) indicated that a period of karst water freezing occurred in marine isotope stage (MIS) 3, within the Weichselian. The cave also hosts numerous examples of speleothem damage. As shown in this paper, some of these are clearly connected with freezing conditions and cave ice action.
A new fossiliferous Upper Pleistocene section located on slopes of the Berounka River valley was found at the village of Stradonice (Beroun District, Czech Republic). The section (marked as A in the text below) lies approx. 35 m above the present-day level of the river. It consists of prevailing mixed eolian-deluvial and eolian sediments with exposed thickness of 90 cm. The finding includes fragments of a horse mandible (Equus ferus germanicus Nehring, 1804), rare mollusks (Pupilla muscorum, Pupilla triplicata, Helicopsis striata) and bones, and bone fragments of small vertebrates (Microtus gregalis/arvalis, Microtus sp.). The collagen of horse bones yielded a calibrated radiocarbon age of 29 366–28 771 BC, chronologically fitting into the Marine Isotope Stage 3 (MIS 3), a period of variable climate prior to the onset of the Last Glacial Maximum. A layer of brown-red soil with cubic to polyhedral structure which may belong to MIS 2 sits on the top of eolian deposits. The exposed section is covered by recent soil containing ceramic shards and animal bones coming from a period stretching from the Middle Ages until today (the oldest bone is 1 458–1 539 cal. AD). Another section (marked as B) lying at a distance of ca 20 m from section A, and 4 m higher, and close to the upper edge of the gorge, was identified. It consists of eolian-deluvial sediments also corresponding to MIS 3, and containing rare mollusks (Pupilla muscorum, Helicopsis striata) and seeds of yew (Taxus baccata). The age of section A can in general be compared to the occurrence of macrofauna found in nearby locality at Hýskov (2 km downstream), located at a similar height above the current river level. On the contrary, the section at Karlštejn-Altán (17 km downstream), developed at the same level, is apparently much older (probably MIS 9–7), and its lithology is also markedly different.
The Ještěd Ridge (part of the Krkonoše-Jizera Crystalline Complex; northern part of the Bohemian Massif) hosts 20 known karst caves, which are developed in marbles of Devonian age. The caves are mostly relatively small and isolated, not connected into larger cave systems. The longest one, Západní (Jitravská) Cave, currently exceeds the length of 450 m. Majority of the known caves are shorter than 50 m. Formation of these cavities was initiated under morphological conditions different from those of today, in the pre-Quaternary. The caves are developed along two systems of regional faults, one striking NW-SE and the second striking SW-NE. One of the newly found caves, about 70 m long Dvoustovka Cave, was discovered in 2015 at an elevation of ca. 795 m a.s.l., close to the Ještěd ridgeline near the Pláně pod Ještědem site. The cave hosts several speleothem types including unusual, coarse-crystalline speleothems characterized by translucent calcite crystals up to 15 mm in size (so-called dogtooth spar). These speleothems developed in several small water pools located at different elevations within the cave. Fluid inclusions and C and O stable isotope studies (Table 1) do not support their deposition from thermal water and indicate formation from usual low-temperature descending karst water. Fluid inclusions in calcite of dogtooth spar are single-phase, containing low-salinity water. The C and O isotope data lie in a range typical of usual low-temperature Quaternary speleothems of the area. The U-series dating (methods: spike addition; dissolution; chromatographic separation using TRU-resin; measurement on ICP-MS; results in Table 2) indicate an age of the coarse-crystalline speleothems fitting into the Eemian interglacial (118 ± 3 ka BP). Underground spaces of the Dvoustovka Cave are affected by numerous movements along cracks and rock collapses. While some of these movements occurred before the formation of the studied coarse-crystalline speleothems, majority of them are younger, related most probably to slope movements (mass wasting) during the last Glacial. The cave cannot keep larger stagnant pools of karst water today.
Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε⁵⁴Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the ⁵⁴Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ¹⁷O values as low as −0.22‰ in irghizites, however, are incompatible with a CI-like impactor. We suggest that the observed ¹⁷O depletion in irghizites relative to the terrestrial range is caused by partial isotope exchange with atmospheric oxygen (Δ¹⁷O = −0.47‰) following material ejection. In contrast, combined Δ¹⁷O–ε⁵⁴Cr data for central European tektites (distal ejecta) fall into the terrestrial range and neither impactor fingerprint nor oxygen isotope exchange with the atmosphere are indicated.
Freezing of karst water in caves forces the segregation of solutes, a process of rejection of dissolved ions by the advancing ice-water front during the growth of ice crystals. This process causes supersaturation of the unfrozen residual part of the solution and precipitation of some of dissolved compounds as minerals. Water evaporation and solution degassing additionally enhance the mineral formation. The cryogenic cave minerals constitute a variety of speleothems, which differ in practically all aspects from their counterparts formed in caves unaffected by freezing. The morphology and mineralogy of cryogenic cave minerals largely depend on the initial chemical composition of the karst water, the thickness of the water layer that freezes, and the freezing rate. The most common cryogenic minerals in the ice caves of limestone karst are fine-grained (powdery) carbonates produced by rapid water freezing in thin water layers. In contrast, slower freezing of large water volumes at cave temperature near 0°C produces coarse-grained cryogenic cave carbonates, which are typically associated with present or past permafrost conditions. Overall, the cryogenic cave carbonates are characterized by C and O isotope signatures different from that of speleothems in temperate environments. Apart from the cryogenic carbonates, several other freeze-related minerals have been identified in caves. By far, the richest diversity of cryogenic minerals occurs in gypsum-hosted ice caves.
The Obří důl Fe–Cu–As polymetallic sulfide skarn deposit is developed in a metamorphic series in the West Sudetes, Bohemian Massif. It consists of lenses of marble, calc–silicate rocks, and skarns. We studied the Gustav orebody, which is located few hundred meters away from the contact with a large, late-orogenic Variscan Krkonoše–Jizera Plutonic Complex (KJPC) emplaced into shallow crust. Mineralogical and fluid inclusion study evidence indicates that the main sulfide stage, dominated by pyrrhotite, arsenopyrite, and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt% NaCl eq. with minimum homogenization temperatures ranging from 324 to 358 °C. These fluids mainly replaced carbonate-rich lithologies. Carbon, oxygen, and strontium isotope data in Ca-rich rocks imply total overprinting by channelized metasomatic fluid flow, which is most probably related to the intrusion of the KJPC, whereas δ34S values of sulfides argue for a magmatic source of sulfur. The Re–Os age of arsenopyrite overlaps published age data for the KJPC and suggests synchronous formation of the main sulfide mineralization and pluton emplacement.
Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = −0.07 to +0.64‰; δ65Cu = −0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts.
Impact processes are natural phenomena that contribute to a variety of physico–chemical mechanisms over an extreme range of shock pressures and temperatures, otherwise seldomly achieved in the Earth’s crust through other processes. Under these extreme conditions with transient temperatures and pressures ≥3,000K and ≥100 GPa, followed by their rapid decrease, the behavior of elements has remained poorly understood. Distal glassy ejecta (tektites) were produced in early phases of contact between the Earth’s surface and an impacting body. Here we provide evidence for a complex behavior of Os and other highly siderophile elements (HSE; Ir, Ru, Pt, Pd, and Re) during tektite production related to a hyper-velocity impact that formed the Ries structure in Germany. Instead of simple mixing between the surface materials, which are thought to form the major source of central European tektites (moldavites), and impactor matter, the patterns of HSE contents and ¹⁸⁷Re/¹⁸⁸Os – ¹⁸⁷Os/¹⁸⁸Os ratios in moldavites, target sediments and impact-related breccias (suevites) can be explained by several sequential and/or contemporary processes. These involve (i) evaporative loss of partially oxidized HSE from the overheated tektite melt, (ii) mixing of target-derived and impactor-derived HSE vapor (plasma) phases, and (iii) early (high-temperature) condensation of a part of the mixed vapor phase back to silicate melt droplets. An almost complete loss of terrestrial Os from the tektite melt and its replacement with extra-terrestrial Os are indicated by low ¹⁸⁷Os/¹⁸⁸Os ratios in tektites (<0.163) relative to precursor materials (>0.69). This is paralleled by a co-variation between Os and Ni contents in tektites but not in suevites formed later in the impact process.
The quarry at Chlum Hill near the Srbsko village, disclosed a series of underground spaces during the first half of the 20th century, including the second largest cave system in the Bohemian Karst of that time. Since the beginning, simultaneously with the speleological exploration, a particular attention was given to the deposits yielding fossil bones collected subsequently by several collectors. These deposits were contained mainly in vertical cavities denoted as „Caverns No. 1 to 8“. We provide a critical survey of these investigations including those from the last two years which essentially refine the current knowledge of the topic. A revision of fossil materials and lithostratigraphic setting of particular localities revealed three distinct stages of Quaternary deposition: (i) the Late Pleistocene stage (probably the Eemian and Early Vistulian) – site Chlum 5=7, (ii) the Early Pleistocene (Q1) stage – sites Chlum 6 and 8, and (iii) a complicated complex of surface and underground deposits covering two or three glacial cycles around the Q2/Q3 boundary (MIS 19-15), denoted herein as Chlum 4 s. l. (incl. Chlum 1 to 4 and a series of surface exposures). The extensive sedimentary complex of Chlum 4 covers the SW slopes of the hill, filling the erosional scarp of the Berounka River terrace 80 m above the present river level as well as the multiple subsurface cavities connected to it. Further investigations of that complex, both speleological and paleontological, are in progress.
Lithium abundances and isotope compositions are presented for a suite of sediments from the surroundings of the Ries Impact structure, paralleled by new Li data for central European tektites (moldavites) from several substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia), including a specimen from the newly discovered substrewn field in Poland. The data set was supplemented by three clay fractions isolated from sedimentary samples. Moldavites measured in this study show a very narrow range in δ7Li values (−0.6 to 0.3‰ relative to L-SVEC) and Li contents (23.9–48.1 ppm). This contrasts with sediments from the Ries area which show remarkable range in Li isotope compositions (from −6.9 to 13.4‰) and Li contents (0.6–256 ppm). The OSM sediments which, based on chemical similarity, formed the major part of moldavites, show a range in δ7Li values from −2.0 to 7.9‰ and Li contents from 5.8 to 78.9 ppm. Therefore, the formation of moldavites was apparently accompanied by large-scale mixing, paralleled by chemical and isotope homogenization of their parent matter. The proposed Li mixing model indicates that sands, clayey sediments, and low volumes of carbonates are the major components for tektite formation whereas residual paleokarst sediments could have been a minor but important component for a subset of moldavites. Striking homogenization of Li in tektites, combined with limited Li loss during impacts, may suggest that moderately volatile elements are not scavenged and isotopically fractionated during large-scale collisions, which is consistent with recent models. In general, whether homogenization of bodies with distinct Li isotope systematics takes place, or collision of bodies with similar Li systematics operates cannot be resolved at present stage but Li isotope homogeneity of solar system planets and asteroidal bodies tentatively implies the latter.
Internal structure and element chemistry including contents of highly siderophile elements (HSE) and Os isotope ratios have been studied in target rocks and several groups of impact glasses of the Zhamanshin impact structure, Kazakhstan. These include larger irregularly-shaped fragments and blocks of impact glass (zhamanshinite), and three types of tektite-like splash-form glasses, part of fallback ejecta. These glassy objects typically are up to 30 mm large and are shaped as teardrops, irregularly bent and curved glass rods and fibers. They can be subdivided into acidic types (irghizites; typically 69–76 wt.% SiO2), basic splash-forms (typically 53–56 wt.% SiO2), and rarely occurring highly inhomogeneous composites with abundant mineral inclusions. A comparison with the target rocks shows that zhamanshinites and basic splash-forms usually have no detectable admixture of the projectile matter, indicated by major and trace elements as well as highly siderophile element contents, with an exception of one sample containing Fe-, Cr-, Ni- and Ti-enriched particles and elevated HSE contents. In contrast, irghizites exhibit clear admixture of the projectile matter, which was incorporated by complex processes accompanied by strong element fractionations. Microscopic investigations confirm that irghizites were formed mainly by coalescence of smaller molten glass droplets sized typically below 1 mm. Irghizites exhibit significant enrichments in Ni, Co and Cr, whose concentrations are locally enriched in the rims of the original small droplets. A portion of these elements and also part of Fe and Mn and other elements were derived from the impactor, most likely a Ni-rich carbonaceous chondrite. The contents of HSE are low and strongly fractionated, with moderate depletions of Pt and Pd and strong depletions of other HSE with respect to chondritic element ratios. Osmium shows the strongest depletion, likely related to the presence of oxygen in the post-impact atmosphere causing strong Os loss through volatilization. One composite splash-form contains Fe–Ni–S inclusions and exhibits a less fractionated HSE pattern suggesting the lowest degree of melting, volatilization and condensation. The observed structural and microchemical features of irghizites are interpreted to reflect variable proportions of the uppermost target sediments and the projectile matter, with HSE element ratios influenced by evaporation and condensation processes, and differences in volatility of individual HSE elements and/or their compounds. Two possible pathways of incorporation of the projectile matter into the irghizites include either re-condensation of evaporated projectile matter on the surface of glass droplets, or incorporation of less chemically fractionated microparticles dispersed by the explosion.
Moldavites, tektites of the Central European strewn field, have been traditionally linked with the Ries impact structure in Germany. They are supposed to be derived mainly from the near-surface sediments of the Upper Freshwater Molasse of Miocene age that probably covered the target area before the impact. Comparison of the chemical composition of moldavites with that of inferred source materials requires recalculation of the composition of sediments to their water-, organic carbon- and carbon dioxide-free residuum. This recalculation reflects the fact that these compounds were lost almost completely from the target materials during their transformation to moldavites. Strong depletions in concentrations of many elements in moldavites relative to the source sediments (e.g., Mo, Cu, Ag, Sb, As, Fe) are contrasted with enrichments of several elements in moldavites (e.g., Cs, Ba, K, Rb). These discrepancies can be generally solved using two different approaches, either by involvement of a component of specific chemical composition, or by considering elemental fractionation during tektite formation. The proposed conceptual model of moldavite formation combines both approaches and is based on several steps: (i) the parent mixture (Upper Freshwater Molasse sediments as the dominant source) contained also a minor admixture of organic matter and soils; (ii) the most energetic part of the ejected matter was converted to vapor (plasma) and another part produced melt directly upon decompression; (iii) following further adiabatic decompression, the expanding vapor phase disintegrated the melt into small melt droplets and some elements were partially lost from the melt because of their volatility, or because of the volatility of their compounds, such as carbonyls of Fe and other transition metals (e.g., Ni, Co, Mo, Cr, and Cu); (iv) large positively charged ions such as Cs+, Ba2+, K+, Rb+ from the plasma portion were enriched in the late-stage condensation spherules or condensed directly onto negatively charged melt droplets; (v) simultaneously, the melt droplets coalesced into larger tektite bodies. Steps (iii) to (v) may have overlapped in time. The still melted moldavite bodies reaching their final size were reshaped by further melt flow. This melt flow was related to moldavite rotation and escape (bubbling off) of the last portion of gaseous volatiles during their flight in a low-pressure region above the dense layer of the atmosphere.
Brdy Highland represents the highest upland in the central part of the Czech Republic outside the mountain ranges distributed in the peripheral parts and along the borders of the country. Because of the existence of a military training ground in its highest part, Brdy Highland is the least known of all the Czech mountains and highlands. Termination of military use of the area by January 2016 opened the area to the public. Quartz-dominated Cambrian conglomerates and sandstones form the highest parts of the highland. The specific lithology of these sedimentary rocks produced extremely infertile, low pH soils. Because of the low fertility, the area was always almost unpopulated, forested and served as source of timber, charcoal and water for mining and ore processing activities in areas at the foot of the highland. Compared to higher mountains distributed along the borders of the Czech Republic, Brdy Highland receives less precipitation and fluvial processes have had a less pronounced effect on its morphology. The relics of pre-Quaternary planated surface forming the summit of the highland were dissected into structural-erosional ridges mainly by processes operating in the periglacial zone of Quaternary glacials . Solifluction on the gentle slopes and frost disintegration of the rock faces were the main processes forming abundant periglacial landforms. Fossil cryoplanation terraces and solifluction lobes , rocks of the tor type, frost-riven cliffs, block fields and block streams are abundant. The possible existence of other fossil features such as patterned ground , nivation hollows or possible rock glaciers requires further study.
Rich in historical heritage and natural beauties and located close to Prague , the Bohemian Karst has attracted visitors and scholars for centuries. Lower Paleozoic strata, folded and faulted during the Variscan Orogeny , have yielded thousands of fossil species . Well-exposed sedimentary rocks enabled definition of five international stratotype and/or parastratotype sections of geological boundaries. Most of the karst forms are inactive and largely sediment-filled (paleokarst ). The area is poor in karren fields, doline s and underground active streams, but rich in complex maze caves , locally with small but deep cave lakes. Morphological evolution of the present-day landscape was initiated after Cretaceous and Paleogene planation, when the area started to be entrenched by low-gradient Oligocene and Miocene rivers. In the Middle and Late Pleistocene, the entrenchment of river valleys was accelerated, forming steep-walled rocky canyons combined with a system of river terraces. Following earlier thermal water karstification , river floodwater injection was the main speleogenetic process during the Neogene and Quaternary. Archaeological finds and human bones up to ca. 150,000 years old have been discovered in the area. Historical sites, like the former Slavic fortified settlement at Tetín, majestic Gothic Karlštejn Castle, the Baroque monastery and church at Svatý Jan pod Skalou, and the hiking and educational trails annually attract approximately half a million visitors.
Moldavites are known to occur in several geographically limited areas in Central Europe: South Bohemia, Western Bohemia (Cheb Basin), Western Moravia, the Horn area in Upper Austria, and Lusatia in Germany. In addition to these traditional finds, Central European tektites (CET) have recently been identified in Neogene sediments at three places in Lower Silesia in Poland. Sandpits near Rusko and Mielęcin represent the most remote localities from the Ries impact structure with the distance of about 475 km. The previously published data were limited to electron-microprobe analyses of four specimens. Here we provide additional compositional data for a single moldavite from the North Stanisław sandpit near Rusko. Combined data of electron microprobe (EPMA; major elements) and laser-ablation inductively-coupled- -plasma mass spectrometry (LA-ICP-MS; minor and trace elements) provide new insights into chemical variability of CET. Electron-microprobe analyses supplemented with back-scattered electron images showed marked chemical heterogeneity of the Polish moldavite on the micrometre scale, confirmed also by LA-ICP-MS. The major-element composition of the volumetrically dominating glass of the specimen is indistinguishable from the majority of c. 5000 available EPMA analyses of moldavites from other regions and, consequently, it does not provide any unambiguous link to any of these sub-strewn fields. Rare schlieren in the sample with unique Ca-Mg-rich composition have counterparts among several South Bohemian moldavites. In general, Polish moldavites are small (less than 0.5 g) irregular fagments or splinters of angular shape with multistage sculpturing. Their morphological character and paleogeography of Central Europe in the last 15 Myr suggest that they were redeposited at time of the Gozdnica Fm. sedimentation from yet unknown sub--strewn field north of the Sudetic Mountains.
The Bohutín Stock is one of several small isolated intrusions occurring in the northern surroundings of the Variscan Central Bohemian PlutonicComplex (Bohemian Massif, Czech Republic). The stock with surface outcrop area of about 3.6 sq. km is known thanks to intensive underground mining of the Bohutín Ag-Pb Zn-Sb vein-type deposit (1841-1979) down to 1350 m below the surface. The Bohutín Stock is a petrographically variable body with quartz diorite or tonalite as the most widespread rock type. More basic diorite to gabbrodiorite enclaves as well as rocks of granodiorite to granite composition (trondhjemite) also occur in the stock. Earlier conventional K-Ar ages of the Bohutín Stock indicated Silurian to Early Devonian age of the intrusion (440-400 Ma) which was rather controversial, since the formation of majority of the Central Bohemian PlutonicComplex covers a period between 354 ± 4 and 337 ± 1 Ma. One later Ar-Ar age determination on amphibole from a gabbrodiorite enclave had excess argon with plateau age of 348.5 ± 0.5 Ma. To solve this controversy, the main intrusive rock type of Bohutín Stock, quartz diorite, was dated by zircon U-Pb method using laser ablation ICP-MS. The dated sample was collected at a depth of 1199 m below the surface. Representative cathodoluminescence images of the dated zircon grains are shown in Fig. 1 and U-Pb concordia diagram for zircons from Bohutín in Fig. 2. Studied quartz diorite from the deeper part of the Bohutín Stock is homogeneous equigranular fine-grained rock composed of (in descending order) subhedral zoned plagioclase (labradorite→oli-goclase), actinolitic amphibole, anhedral biotite, quartz, and K-feld-spar. For chemical composition of studied sample see Table 1. The obtained U-Pb zircon concordant age of 344.2 ± 0.6 Ma (for data of individual zircon grains see Table 2) is close to the age of zircons from granodiorite of the nearby Padr͖ Stock (342.8 ± 1.1 Ma). Both small intrusions therefore probably intruded in the same phase of structural evolution of the complex boundary zone between Moldanubian Unit and Bohemicum. Their age is within the age range of the main intrusive masses of the Central Bohemian Plutonic Complex.
Coupled Ca-Mg-Si isotope data delimit the roles of individual sediment types that formed tektite melts and distinguish between kinetic and equilibrium effects.
Gravitational mass movements (landslides) have been one of the most efficient processes contributing to the morphogenesis of the Outer Carpathians formed of flysch, siliciclastic-clayey rocks. Such processes often produce non-karst caves in sandstones. Dating of calcite speleothems developed in caves hosted by sandstone with calcareous cement seems to be a suitable method to reconstruct phases of slope evolution in this region. The paper discusses the usefulness of radiocarbon (14C) and U-series dating of speleothems in non-karst caves in the reconstruction of mass movement chronology and evaluates possible reasons for discrepancies between both methods. The obtained speleothem age data are used to improve the existing knowledge on the chronology of mass movements during the Late Glacial and Holocene in the flysch Carpathians.
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 Central Bohemian 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).
The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite δ18O data show an irregular decrease from values reaching up to +1.6‰ in the Middle Oxfordian and from +0.8 to −1.7‰ in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon δ13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.
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 ~ 335 Ma 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 ± 1.5 Ma 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 341 Ma and 340 to 337 Ma. 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).
The Carpathian Mountains across Slovakia and Romania are home of several ice caves located at elevations between 700 and 1,200 m above sea level (asl). Although the mean surface annual temperature is above the freezing point, perennial ice deposits are common in caves and shafts with certain morphologies (large entrances followed by steep vertical or downward-sloping passages), into which the dense cold winter air sinks and remains trapped all year round. A particular type of cave pearls (cryogenic cave pearls, CCPs) occur in spatially restricted accumulations or extensive pearl fields (layers locally up to 0.5 m in thickness) within the scree covering the cave floor in the periglacial zone of these caves. The temperature in the periglacial zone oscillates around the freezing point, promoting seasonal ice formation. A similar type of pearl is observed in the entrance section of other caves that experience temporary freezing conditions during the cold season. When compared to pearls of non-iced caves, those from ice caves always occur at sites where liquid water cannot accumulate. CCP formation in nests with drips or in cave pools surrounded by rimstone dams is therefore excluded. Freezing thawing processes are responsible for moving the pearls, preventing their cementation to the floor or between them. Results of U-series and radiocarbon dating indicate that the pearls are Holocene in age, with their growth continuing into the present. Pearls show high porosity, ranging from 7.6 to 22.6%. In the center they frequently contain radial aggregates of larger carbonate crystals, and their concentric layering is less obvious compared to normal cave pearls. In addition, polygonal pearls and pearl aggregates are common. Stable carbon and oxygen isotope study indicates the formation. of an initial crystal aggregate by cryogenic precipitation during freezing of drip water. After that, pearls grow by addition of new carbonate layers, either at water freezing conditions or at temperature above 0 degrees C. Overall, the pearl isotope data plot along a mixing line in the delta C-13 vs. delta O-18 diagram, connecting the field of normal speleothems of non-iced caves of the area, with the field of fine-grained cryogenic carbonate powder, formed in the glaciated parts of the ice caves. Seasonal water freezing and frost action in the cave periglacial zone is a necessary condition for the formation of these pearls.
Cryogenic cave carbonate (CCC) represents a specific type of speleothem whose precipitation is triggered by freezing of mineralized karst water. Coarsely crystalline CCC, which formed during slow freezing of water in cave pools, has been reported from 20 Central European caves located in Germany, the Czech Republic, Slovakia and Poland. All these caves are situated in an area which was glacier-free during the Weichselian. Whereas the formation of usual types of speleothems in caves of this region usually ceased during the glacials, coarsely crystalline CCC precipitation was restricted to glacial periods. Since this carbonate type represents a novel, useful paleoclimate proxy, data from its Weichselian occurrences in caves in Central Europe were collected, including their C and O stable isotope values, U-series ages and depth below the surface. When using only the CCC data from caves with limited cave ventilation, the permafrost depths of the Weichselian can be estimated to be at least 65 m in the lowlands and uplands. An isolated CCC find indicates that Weichselian permafrost penetrated to a depth of at least 285 m in the High Tatra mountains, Slovakia. A model of the formation of coarsely crystalline CCC assumes its formation especially during periods of permafrost thawing. U-series data confirm that permafrost depth changed and CCC precipitation in deep caves occurred repeatedly in the studied area during marine isotope stages 4, 3 and 2. One important phase of coarsely crystalline CCC formation related to permafrost thawing occurred between 40 and 21 ka BP, and the last phase of its formation was related to the final permafrost destruction between 17 and 12 ka BP.
Tektites, natural silica-rich glasses produced during impact events, commonly contain bubbles. The paper reviews published data on pressure and composition of a gas phase contained in the tektite bubbles and data on other volatile compounds which can be released from tektites by either high-temperature melting or by crushing or milling under vacuum. Gas extraction from tektites using high-temperature melting generally produced higher gas yield and different gas composition than the low-temperature extraction using crushing or milling under vacuum. The high-temperature extraction obviously releases volatiles not only from the bubbles, but also volatile compounds contained directly in the glass. Moreover, the gas composition can be modified by reactions between the released gases and the glass melt. Published data indicate that besides CO2 and/or CO in the bubbles, another carbon reservoir is present directly in the tektite glass. To clarify the problem of carbon content and carbon isotopic composition of the tektite glass, three samples from the Central European tektite strewn field—moldavites—were analyzed. The samples contained only 35-41 ppm C with δ13C values in the range from -28.5 to -29.9‰ VPDB. This indicates that terrestrial organic matter was a dominant carbon source during moldavite formation.
Cryogenic cave carbonate (CCC) represents a specific type of speleothems, whose precipitation is triggered by freezing of mineralized karst water. Coarse-crystalline CCC, which formed during slow freezing of water in cave pools, is known in 20 Central European caves located in Germany, the Czech Republic, Slovakia and Poland. All these caves are situated in an area, which was glacier-free during the Weichselian. Whereas the formation of usual types of speleothems in caves of this region usually ceased during glacials, CCC precipitation was restricted to glacial periods. Since CCC represents a novel, useful paleoclimate proxy, data from Weichselian CCC occurrences in caves in Central Europe were collected, including their C and O stable isotope systematics, U-series ages and depth below the surface. When using only the CCC data from caves with limited cave ventilation, the permafrost depths of the Weichselian can be estimated to be at least 65 m in the lowlands and uplands. An isolated CCC find indicates that Weichselian permafrost penetrated to a depth of at least 285 m in the High Tatra Mts., Slovakia. A model of the formation of coarse-crystalline CCC assumes its formation especially during periods of permafrost thawing. U-series data confirm that permafrost depth changed and CCC precipitation occurred repeatedly in the studied area during Marine Isotope Stages 4, 3 and 2. One important phase of CCC formation related to permafrost thawing occurred between 40 and 21 ka BP, and the last phase of its formation was related to the final permafrost destruction between 17 and 12 ka BP.
Hydraulic and hydrochemical relationships between a medium gradient river and a karst aquifer were studied by water level and temperature logging combined with water geochemistry and delta C-13. The cave lakes are separated from the river by a floodplain up to 150 m wide formed by a gravel and sand layer up to 13 m thick covered with fine-grained floodplain sediments. During minor discharge peaks (water level in the river < 1.5 m above the normal river stage), a water level oscillation in the cave lakes situated 40 to 190 m away from river is induced by the river level oscillation, but the river water does not enter any of the lakes. The groundwater chemistry in the cave lakes differs from that of the river water. Low bicarbonate content and high delta C-13 values indicate that some of cave lakes' waters have undergone CO2 degassing and calcite precipitation. During a major flood (recurrence interval > 100 years, level rising 7 m above the normal stage), the river water rapidly flooded the caves through openings in the river canyon (flood-flow injection), while those connected to the river via alluvium only were flooded by an elevated groundwater stage, and the resulting water level rise was only about 50 percent of the river level increase. A simple hydraulic model was successfully used to simulate and explain the water table oscillations in the cave lakes. Flood-flow injection has recently been substantially reduced by low-permeability, fine-grained late Holocene fluvial sediments that cap coarse gravels in the river floodplain. Fast speleogenesis by flood injection would be expected in periods when the river canyon was bare or filled by gravel alone (glacial periods, transition to Holocene). Ice jams causing local increases in the river level are recognized as one of factors that can be important in speleogenesis.
An investigation of the thermal waters in the Ústí nad Labem area in the northeastern part of the Eger Rift has been carried out, with the principal objective of determining their origin. Waters from geothermal reservoirs in the aquifers of the Bohemian Cretaceous Basin (BCB) from depths of 240 to 616 m are exploited here. For comparison, thermal waters of the adjacent Teplice Spa area were also incorporated into the study. Results based on water chemistry and isotopes indicate mixing of groundwater from aquifers of the BCB with groundwater derived from underlying crystalline rocks of the Erzgebirge Mts. Unlike thermal waters in Děčín, which are of Ca–HCO3 type, there are two types of thermal waters in Ústí nad Labem, Na–HCO3–Cl–SO4 type with high TDS values and Na–Ca–HCO3–SO4 type with low TDS values. Carbon isotope data, speciation calculations, and inverse geochemical modeling suggest a significant input of endogenous CO2 at Ústí nad Labem in the case of high TDS groundwaters. Besides CO2 input, both silicate dissolution and cation exchange coupled with dissolution of carbonates may explain the origin of high TDS thermal waters equally well. This is a consequence of similar δ13C and 14C values in endogenous CO2 and carbonates (both sources have 14C of 0 pmc, endogenous CO2 δ13C around −3‰, carbonates in the range from −5‰ to +3‰ V-PDB). The source of Cl− seems to be relict brine formed in Tertiary lakes, which infiltrated into the deep rift zone and is being flushed out. The difference between high and low TDS groundwaters in Ústí nad Labem is caused by location of the high mineralization groundwater wells in CO2 emanation centers linked to channel-like conduits. This results in high dissolution rates of minerals and in different δ13C(DIC) and 14C(DIC) fingerprints. A combined δ34S and δ18O study of dissolved SO4 indicates multiple SO4 sources, involving SO4 from relict brines and oxidation of H2S. The study clearly demonstrates potential problems encountered at sites with multiple sources of C, where several evolutionary groundwater scenarios are possible.
The stable isotope record and diversity of Cenomanian and Turonian rudists were compared for areas located at low paleolatitudes (10°N - Northern Egypt; 5 samples; 13 analyses) and middle paleolatitudes (35°N - Czech Republic, Bohemian Cretaceous Basin, BCB; 4 samples; 7 analyses). The oxygen isotope data indicate that the δ18O value of seawater was not identical for both areas. Moreover, local variations in seawater δ18O in the range of at least ±1‰ are probable in the shallow water near-shore environment where the rudists lived. Supposing a value of -1‰ VSMOW for contemporaneous seawater, the paleotemperature can be calculated as being between 24.5 and 31.5 °C for the Late Cenomanian and between 32.9 and 34.7 °C for the Early Turonian in the BCB. The δ18O seawater value for the northern part of Egypt was probably slightly lower. Calculation using a seawater value of -1.5‰ VSMOW gives temperatures for the Egypt in the range of 31.0 to 38.8 °C for the Late Cenomanian and 35.5 to 41.2 °C for the Turonian. The sclerochronological isotope profiles within one shell show changes of the calcite δ18O value, probably reflecting seasonal changes, with the largest observed within-shell temperature shift corresponding to 8 °C. The analyzed pilot sample set shows that the BCB and Egyptian rudists contain valuable paleoenvironmental information and that a detailed isotope study is needed. Rudist generic diversity of both areas was also compared. The Cenomanian and Turonian rudist assemblages from Egypt and the BCB show similar generic diversity, and also display a similar marked diversity decrease across the Cenomanian/Turonian boundary interval. It is important to note that both areas have similar diversity on the generic and partially species level during the Cenomanian and Turonian.
Metal mining and processing in the central Czech Republic has led to the contamination of surrounding soils and vegetation. In this study, Hg concentrations were measured in spruce (Picea abies L.) and beech (Fagus sylvatica L.) tree rings to monitor historical Hg deposition in the area. The highest Hg concentrations were found in spruce at an HgS smelting contaminated site (up to 15ngg−1), probably reflecting smelting activities at the end of the nineteenth century. In the vicinity of a Pb smelter, Hg concentrations increased from the 1950s to maxima (up to 8.4ngg−1) in the 1970s, corresponding with a peak of metallurgical production and smelter emissions in the mid 1970s. A decreasing trend in Hg concentrations since the 1980s was probably related to improvements in flue gas cleaning technologies. The beech trees, which grow at a site between two smelters and range in age from 150 to 220years, seem to reflect deposition from both point sources. Mercury levels in beech trees were lower, that resulting from their greater distance from pollution sources, but the concentration trend was strongly correlated with metal production. Analysis of nutrient elements (Ca, Mg, K and Mn) in wood revealed environmental changes related to acid deposition, but a relation between concentration trends of nutrients and Hg was not found. This study shows that tree rings may be a good record of Hg deposition in areas affected by ore mining and smelting. Nevertheless, further investigation of Hg cycling in trees is necessary to satisfactorily interpret this particular historical Hg record. KeywordsMercury–Dendrochemistry–Trees–Geochemical archives–Czech Republic
Carbon and oxygen stable isotope records were compared for Jurassic/Cretaceous (J/K) boundary sections located in the Tethyan Realm (Brodno, Western Slovakia, and Puerto Escaño, Southern Spain; bulk limestones), and the Boreal Realm (Nordvik Peninsula, Northern Siberia, belemnites). Since a detailed biostratigraphic correlation of these Tethyan and Boreal sections is impossible due to different faunal assemblages, correlation of the isotope records was based on paleomagnetic data. This novel approach can improve our understanding of the synchroneity of individual isotope excursions in sections where detailed biostratigraphic correlation is impossible. No significant excursions in either the carbon or oxygen isotope records to be used for future Boreal/Tethyan correlations were found around the J/K boundary (the upper Tithonian and lower Berriasian; magnetozones M20n to M18n) in the studied sections. At the Nordvik section, where a much longer section (middle Oxfordian–basal Boreal Berriasian) was documented, the transition from the middle Oxfordian to the Kimmeridgian and further to the Volgian is characterized by a decrease in belemnite δ18O values (from δ18O values up to + 1.6‰ vs. V-PDB in the Oxfordian to values between + 0.3 and − 0.8‰ in the late Volgian and earliest Boreal Berriasian). This trend, which has previously been reported from the Russian Platform and Tethyan Realm sections, corresponds either to gradual warming or a decrease in seawater δ18O. Supposing that the oxygen isotope compositions of seawater in the Arctic/Boreal and Tethyan Realms were similar, then the differences between oxygen isotope datasets for these records indicate differences in temperature. The Boreal/Tethyan temperature difference of 7–9 °C in the middle and late Oxfordian decreases towards the J/K boundary, indicating a significant decrease in latitudinal climatic gradients during the Late Jurassic. Two positive carbon isotope excursions recorded for the middle Oxfordian and upper Kimmeridgian in the Nordvik section can be correlated with a similar excursion described earlier for the Russian Platform. Minor influence of biofractionation at the carbon isotopes, and the influence of migration of belemnites to deeper, slightly cooler water at the oxygen isotopes, cannot be excluded for the obtained belemnite data.
Stratabound barite and celestite deposits, related mainly to three evaporitic sequences, occur in the Mesozoic Neuquen Retroarc Basin, developed to the east of the Andean Cordillera of western Argentina. This basin is filled with Jurassic and Cretaceous marine to continental sediments that unconformably overlie basement rocks of Paleozoic to Triassic age.Celestite deposits formed by initial precipitation from seawater, with later crystallization during diagenesis and recrystallization related to Eocene intrusive activity. This is supported by evidence of evaporitic associations, textures, and Sr and S-isotope data. The barite deposits were deposited in a near-shore environment and could have formed as a result of interaction between barium absorbed in clay minerals (derived from weathering of basement rocks) and hypersaline seawater. This genetic model is supported by evidence such as the stratabound setting, textures, and Sr and S-isotope data.Carbon and oxygen-isotopic compositions of carbonates, which are interbedded with celestites, are in the range expected for marine carbonates. Lead-isotopic compositions of galenas from bedded and vein barite deposits of Upper Jurassic and Lower Cretaceous ages are consistent with Pb remobilization from a source located at high levels of the upper crust, possibly the basement rocks.
The Litavka River (length 56km, watershed area 630km2, average flow at the outlet to the Berounka River 2.57m3 s−1) drains the historical mining, ore processing, and smelting region of Příbram. This Ag–Pb–Zn±Sb ore district (production from the thirteenth century to 1978, locally to 1980) is known for extensive heavy metal contamination. Recent contamination of the Litavka River system is mostly related to the erosion of contaminated soils and fluvial floodplains sediments, especially from a low-gradient river section located immediately below the ore district, where the fine-grained floodplain sediments are from 1.0 to 1.7m thick. Radiocarbon accelerator mass spectrometry dating of charcoal fragments separated from one floodplain profile showed calibrated 14C age in the range AD 1220–1284 at a depth of 1.2m below the surface, while depths of 0.4 and 0.8m yielded ages in the range AD 1680–1939. Formation of this floodplain was related to disturbance of the river equilibrium resulting from deforestation and the influx of fine-grained material from ore processing, including historical failures of settling ponds. Fluxes of heavy metals during flood events in the Litavka River were studied 35km downstream below the ore district. Metals are transported here mostly (more than 99% for Pb) in the form of suspended particulate matter (SPM), which at the outlet of the Litavka River contains 2,016mg kg−1 Zn, 918mg kg−1 Pb, and 25.5mg kg−1 Cd on average. During a snowmelt-related minor flood event between March 25 and 29, 2006 (peak flow 36.6m3 s−1), the river transported 2,400tonnes of SPM during 4days, containing 74kg of Cd, 2,954kg of Pb, and 5,811kg of Zn. During larger floods (water flows above 55m3 s−1 have occurred here 27 times during the last 77years), the contamination is more diluted by material eroded in the floodplain along the middle and lower river course.
Cold Wind Cave, located at elevations ranging between 1,600 and 1,700 m a. s. l. in the main range of the Nízke Tatry Mountains(Slovakia), is linked in origin with the adjacent Dead Bats Cave. Together, these caves form a major cave system located within anarrow tectonic slice of Triassic sediments. Both caves have undergone complex multiphase development. A system of sub-horizontalcave levels characterized by large, tunnel-like corridors was formed during the Tertiary, when elevation differences surroundingthe cave were less pronounced than today. The central part of the Nízke Tatry Mountains, together with the cave systems, wasuplifted during the Neogene and Lower Pleistocene, which changed the drainage pattern of the area completely. The formation ofnumerous steep-sloped vadose channels and widespread cave roof frost shattering characterized cave development throughout theQuaternary.In the Cold Wind Cave, extensive accumulations of loose, morphologically variable crystal aggregates of secondary cave carbonateranging in size between less than 1 mm to about 35 mm was found on the surface of fallen limestone blocks. Based on the C andO stable isotope compositions of the carbonate (δ13C: 0.72 to 6.34 ‰, δ18O: –22.61 to –13.68 ‰ V-PDB) and the negative relationbetween δ13C and δ18O, the carbonate crystal aggregates are interpreted as being cryogenic cave carbonate (CCC). Publishedmodels suggest the formation of CCC in slowly freezing water pools, probably on the surface of cave ice, most probably duringtransitions from stadials to interstadials. Though the formation of these carbonates is likely one of the youngest events in thesequence of formation of cave sediments of the studied caves, the 230Th/234U ages of three samples (79.7±2.3, 104.0±2.9, and180.0±6.3 ka) are the oldest so far obtained for CCC in Central Europe. This is the first description of CCC formation in one caveduring two glacial periods (Saalian and Weichselian).
Fluvial kaolinitic unsorted sands to slightly lithified sandstones were found in an excavation between Měňany water-pumping station and water reservoir near Tobolka village. These sands overlie weakly weathered Lower Devonian limestones at about 390 to 395 m a. s. l. The relic is relatively thin and follows the Tobolka Fault. Stratigraphic correlations are unclear. The assemblage of heavy minerals is composed dominantly of Ti-rich minerals (ilmenite and products of its decomposition, less frequent are rutile, anatase and titanite; 66.1 %). Other minerals include zircone (13.7 %), tourmaline (6 %) and minor amounts of sillimanite, kyanite, staurolite and spinelids (total of 5.5 %). Heavy mineral assemblage is very close to those from Upper Cretaceous sediments (zircone, rutile, Ti and Fe secondary minerals), nevertheless it contains also some typical Tertiary (Miocene) elements (andalusite, kyanite, silimanite). Higher degree of lithification and the lithological character of sands and sandstones are very similar to paleontologically dated Upper Cretaceous deposits belonging to the Peruc Member (Cenomanian) found in nearby quarries.
Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K-Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K-Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K-Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to 264.0 ± 4.3 Ma and roughly correspond with the results of chemical U-Pb dating of authigenic monazite (268 ± 50 Ma). The uranium ore deposition was accompanied by large-scale decomposition of biotite and pre-ore chlorite to Fe-rich illite and iron hydrooxides. Therefore, it is proposed that the deposition of uranium ore was mostly in response to the reduction of the ore-bearing fluid by interaction with ferrous iron-bearing silicates (biotite and pre-ore chlorite). The Th data on primary, mostly aqueous, inclusions trapped in carbonates of the ore substage range between 152°C and 174°C and total salinity ranges over a relatively wide interval of 3.1 to 23.1 wt% NaCl eq. Gradual reduction of the fluid system during the post-ore substage is manifested by the appearance of a new generation of authigenic chlorite and pyrite. Chlorite thermometry yielded temperatures of 150°C to 170°C. Solid bitumens that post-date uranium mineralization indicate radiolytic polymerization of gaseous and liquid hydrocarbons and their derivatives. The origin of the organic compounds can be related to the diagenetic and catagenetic transformation of organic matter in Upper Stephanian and Permian sediments. (3) K-Ar ages on illite from post-uranium quartz-carbonate-sulfide mineralization range from 233.7 ± 4.7 to 227.5 ± 4.6 Ma and are consistent with the early Tethys-Central Atlantic rifting and tectonic reactivation of the Variscan structures of the Bohemian Massif. A minor part of the late Variscan uranium mineralization was remobilized during this hydrothermal event.
The Gunga barite deposits occur in carbonate clastic marine sequence of Jurassic age. These rocks are widely spread in Khuzdar-Lasbela belt which host important stratabound barite and zinc-lead deposits of Pakistan. These rocks are intricately folded and extensively faulted. The Gunga are low temperature hydrothermal deposits occurring as a series of disconnected lenses a few meters thick. Two mineralized horizons are recognized: barite in the upper zone, sphalerite and galena in the lower zone. Four types of barite mineralization occurs in Gunga stratabound replacement associated with 1) fracture filling, 2) open space fillings in solution collapsed breccia, 3) replacement in fault, and 4) veinlets associated with all these three types. The wall rocks of the Gunga deposits have also been altered by silicification, leaching and ferruginization. The sulfur isotope values of most of the Gunga barite samples range from 23.8 to 27.8 per mil with an average of 26.4 per mil, which is very close to the average of isotopic values of epigenetic carbonate hosted Late Paleozoic Missouri barite deposits. The Gunga like other barite and sulfide deposits of Khuzdar-Lasbela belt are Mississippi Valley type, stratabound and of replacement origin precipitated from connate brines expelled during the incipient rifting of India from Gondwana land in the Late Jurassic and Early Cretaceous periods. The low content of copper, lead and zinc in the Gunga barite deposits suggests that these deposits were not formed in proximity to an igneous source of the ore solution. The Gunga deposits are epigenetic and stratabound as their mineralization is structure controlled. There is an evidence of transgressive nature of host rock and wall rock alteration which are absent in stratiform or bedded deposits.
Fine-grained floodplain sediments of the catastrophic 2002 flood deposited along the lower reaches of the Berounka and Vltava Rivers, Czech Republic, were not highly contaminated with heavy metals and other toxic elements. This is due to the dominantly mineral character of the sediments (Ctot in the range 3.97–5.01%, relatively low content of clay minerals), and due to the very high degree of contamination dilution by eroded pre-industrial non-contaminated floodplain sediments. Despite this high degree of dilution, the influence of the small Litavka River, draining the historical Pb–Zn–Ag Příbram ore region, is well visible. The Litavka River is one of important sources of Pb and Zn contamination in the whole Berounka–Vltava–Labe river system. The 2002 flood sediments deposited in the floodplain of the Berounka and Vltava Rivers show poor vertical chemical zoning, except for some components enriched in the uppermost layer by precipitation from evaporated pore-water contained in the mud, i.e. secondary carbonate. The content of Ccarb of the sediments (0.05–0.15%) is partly represented by this secondary carbonate, which is later leached by rainwater, and partly by fragments of river mollusk shells. A majority of the heavy metals contained in sediments can be readily leached by diluted acids, and to a much smaller degree by rainwater.
In the periods 1980–1986 and 1990–2007 many boreholes were sunk during hydrogeological investigations in the center of the Karlovy Vary (Carlsbad) hot spring system. The extent and the depths reached were the greatest in the history of the geological investigation of the discharge area of the thermal system. The results of the drilling program enabled a detailed study of the rocks, groundwater and spring sedimentation in the area as well as the preparation of new proposals for changes in the spring-protection zones. The spring sedimentation consists of world-renowned hot spring travertine, with a wide range of morphological varieties of different origins and of different ages. The oldest U-series age data (230±14ka BP) have been obtained for travertine relicts located 22m above the present-day bottom of the narrow valley of the Teplá River. Five other travertine deposits, partly overlapping in space and time were identified on the bottom and slopes of the valley. They were formed by gradual growth, by river erosion and since the fourteenth century by human activities.
Cryogenic cave carbonate (CCC) represents a specific type of speleothem. Its precipitation proceeds at the freezing point and is triggered by freezing-induced concentration of solutes. Compared to classical speleothems (stalagmites, flowstones), CCC occurs as accumulations of loose uncemented aggregates. The grain sizes range from less than 1 μm to over 1 cm in diameter. Karst groundwater chemistry and its freezing rate upon entering the cave are responsible for highly variable grain morphology. Rapid freezing of water results in the formation of CCC powders with grain size typically below 50 μm. Slow freezing of water in caves (usually in systems where the CO2 escape is partly restricted; e.g., ice covered water pools) results in the formation of large mineral grains, with sizes from less than 1 mm to about 20 mm. The range of carbon and oxygen stable isotope compositions of CCC is larger than for a typical carbonate speleothem. Rapid freezing of water accompanied by a quick kinetic CO2 degassing results in large ranges of δ13C of the CCC powders (between –10‰ and +18‰ PDB). Slow freezing of water, with a restricted CO2 escape results in gradual increase of δ13C values (from −9‰ to +6‰ PDB; data ranges in individual caves are usually much more restricted), accompanied by a δ18O decrease of the precipitated carbonate (overall range from −10‰ to −24‰ PDB). These unusual trends of the carbonate δ18O evolution reflect incorporation of the heavier 18O isotope into the formed ice. New isotope data on CCC from three Romanian ice caves allow better understanding of the carbon and oxygen isotope fingerprint in carbonates precipitated from freezing of bulk water. CCCs are proposed as a new genetic group of speleothems.
Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni-Mo-platinum group elements (PGE)-Au phosphate- and sulfide-rich ores. These are confined to a ≥0.2-m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate- and organic matter-rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100-fold), As (up to 97-fold), Mo (up to 95-fold), Sb (up to 67-fold), Rh (up to 49-fold), Cu (up to 37-fold), Pd (up to 33-fold), Ru (up to 24-fold), Zn (up to 23-fold), Pt (up to 21-fold), Ir (up to 15-fold), Co (up to 14-fold), and Pb (up to 13-fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21-fold) and Ni (12-fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (Corg) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni-, V-, Cr-, and Cu-enriched phosphate-rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal-rich hardground during weathering. The polymetallic Ni-Mo-PGE sulfide-rich ore bed is interpreted to represent a remnant of shallow-water hardground horizon rich in metals, which originated in a sediment-starved, semi-restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi-restricted basin, resulted in the formation of dense metalliferous brines; co-precipitation of metals together with phosphates and sulfides occurred at or above the oxic–anoxic sediment interface. Metal-enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni-Mo-PGE-Au sulfide ore bed, economic sedimentary exhalative (SEDEX)-type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX-type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni-Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals.
Barite occurrences related to the Cenozoic (Late Alpine) low-temperature hydrothermal activity are present in the continental Ohře (Eger) Rift area. A specific, Ra-bearing type of barite has been known under the name “radiobarite” from this area since 1904. Revision of 12 localities revealed the presence of alleged radiobarite only in the Teplice (Lahošť–Jeníkov) and Karlovy Vary areas. Barite from other localities is radium-poor. Barite crystals showing concentric oscillation colour zoning totally prevail. Isomorphous substitution of Sr (X×10−1 to X×wt%), Ca (X×10−2wt%) and Fe (X×10−1wt%) for Ba was proved. Average SrO contents of 0.4wt% are markedly exceeded in some samples from Lahošť–Jeníkov (max. 3.2wt%) and Karlovy Vary (max. 4.9wt%). Besides inclusions of stoichiometric iron disulphide, the same samples also contain iron disulphides with unusual high contents of Co (max. 12.2wt%) and Ni (max. to 8.4wt%). Specific activity of 238U in the studied barites is very low while that of 226Ra reaches 8Bq/g in several samples. Therefore, 226Ra is not in equilibrium with its parent uranium. These “radiobarites” or their parts must be therefore relatively young, not older than 10–15ka. Very low uranium contents (
The first set of U-series ages of the hot-spring travertine from the world-famous Karlovy Vary Spa indicates repeated growth of the travertine accumulation followed by its erosion by the Teplá River. The obtained data are important as an estimate of minimum duration of thermal water circulation in Karlovy Vary and in understanding of the river valley evolution during the youngest geological history. The oldest 230Th/234U age data (230 ± 14 ka BP and 155 ± 7 ka BP) have been obtained for travertine relicts located 22 m above the present-day bottom of the valley. The extensive travertine accumulation located directly on the valley bottom was formed by gradual growth, particularly during the first half of the Weichselian period, between 100 and 50 ka BP. These data show that the valley bottom was at approximately the same elevation as it is today already during the Eemian interglacial. At the end of the Weichselian the central part of the travertine accumulation was downcut by river erosion. During Holocene the new deposition of travertine was concentrated in this wide trench, being likely repeatedly modified by river activity. The travertine accumulation started to be strongly influenced by humans since the Middle Ages. A significant part of it was quarried out for lime production. The accumulation was later covered by buildings, streets and the reinforced course of the Teplá River.
An unusual type of paleokarst carbonate sedimentary rock has been found in the Bohemian Karst, Czech Republic. This well-layered coarse-crystalline limestone is reddish in color and occurs as horizontal or slightly inclined layers filling deep paleokarst cavities within karstified faults in Early Devonian marine-limestone host rocks. Field observations confirm that these sedimentary rocks are undoubtedly younger than the polyphased Variscan folding. Petrographic and geochemical studies indicate that the studied paleokarst limestone is quite different from the Silurian and Devonian limestones, from common cave speleothems, as well as from the typical clastic Late Cretaceous and Cenozoic karst sediments of the Bohemian Karst. Carbonate δ13C and δ18O stable isotopic ratios of the paleokarst limestone (δ13C from –4.0 to –6.2 ‰, δ18Ofrom –6.2 to –8.4‰PDB), differing both from marine Silurian and Devonian limestones and Cenozoic secondary cave carbonates of the area, correspond to a non-marine depositional environment. The paleomagnetic data suggest that magnetic properties of the studied rocks were acquired during the Early to Middle Triassic, although these ages have not yet been confirmed by finds of contemporaneous microfossils. The only microfossils that were extracted using dissolution methods consist of several younger plant and faunal remains including angiosperm pollen grain specimens belonging to the family Myricaceae, likely Tertiary in age. Their sporadic occurrence is interpreted as the result of secondary infiltrations into the millimeter-wide cracks and cavities, in correspondence with the thin-section data on diagenetic successions.
The paper reports the laboratory analyses of the calcite speleothems (stalactites, flowstonesanddripstones)whichoccurr in the pseudokarst caves of Mt. Kilanowska in the Beskid Niski Mts. (flyschCarpathians).Thespeleothemsofthe Jaskinia Słowiańska-Drwali cave have been subjected to detailed studies. The cave (599 m long and 23,8 m deep) is characterised by a relatively stable microclimate similar to static cold caves, with slow cave ventilation. The speleothems occur in its upper part. Performed U-series and radiocarbon datings document the Holocene age of the speleothems. The calcite δ13C and δ18O values are within the range typical for normal Holocene calcite speleothems from the karst caves of central Europe. From a geochemical point of view the formation of speleothem was identical to the normal processes operating in karst. Water evaporation however, was not an important process during the speleothem formation, which could have been conditioned by the limited ventilation of the cave. The deposition of calcite did not always occur under isotopic equilibrium. Periods of rapid kinetic CO2 escape from the solution probably partly influenced the deposition of calcite.
Middle and Upper Pleistocene bone accumulations in caves of the Bohemian Karst, Czech Republic, are newly classified as several types of hyena dens or hyena bone deposits, and cave bear dens. This new taphonomical and paleoecological interpretation of localities that have been known for decades is based on revision of available bone collections, additional field observations at existing localities, and on comparisons with recent spotted hyenas. The thousands of bones from this region, including about seven hundred Pleistocene hyena remains, are strongly frag-mented by having been cracked and chewed, consistent with typical hyena activities. The localities can be subdi-vided chronologically as Middle and Upper Pleistocene, or taphonomically as horizontal and vertical caves and karst depressions. Horizontal and vertical caves show contrasting types of bone accumulations. Several vertical cavities were filled in the Middle Pleistocene and contain the remains of Pachycrocuta brevirostris and its prey. This is the case of the areas of Srbsko–Chlum and Koněprusy–Zlatý Kůň Hill. In the Upper Pleistocene, at least eight caves in the Bohemian Karst were used by hyenas of Crocuta crocuta spelaea as dens and prey storage, some of which were also used by cave bears for hibernating. Upper Pleistocene cave bears were scavenged postmortally by Ice Age spotted hyenas at four cave sites, where they left cracked and chewed Ursus spelaeus bones. Hyenas also stored the remains of their prey in the caves. These remains also include rests of other hyenas, which indicates can-nibalism. Fecal pellets were used for marking the den sites. The Nad Kačákem Cave near Hostim is shown to have been a frequented hyena den based on the presence of many “nibbling sticks” and the remains of juvenile hyena bones. Many hyena skeletons of C. c. spelaea, including juveniles and adults, their coprolites, and the partly cracked bones of their stored prey, were found in vertical caves such as Srbsko–Chlum–Komín. The most spectacu-lar finds are a nearly complete skeleton of the female steppe lion Panthera leo spelaea and an embryo of the Przewalski horse Equus ferus przewalskii. A nearly complete hyena skeleton in the Koněprusy Caves–Prošek Dome is another remarkable find. The most bone-rich localities at Koněprusy–Zlatý Kůň Hill and Srbsko–Chlum Hill are located on, or close to, exposed hill tops, where hyenas had an overview of the surrounding landscape. Sta-tistical analysis of the remains shows that the main animals preyed upon by Upper Pleistocene hyenas were Equus ferus przewalskii and Coelodonta antiquitatis. Additionally, the hyenas fed on Bison priscus, Rangifer tarandus, Cervus elaphus, Megaloceros giganteus, Equus hydruntinus, the Bohemian alpine fauna including Rupricapra rupricapra and Capra ibex, and even the carnivores Ursus spelaeus, Panthera leo spelaea, Canis lupus and possi-bly Gulo gulo. The very few remains of the mammoth Mammuthus primigenius seem to indicate its scarcity in the hilly Bohemian Karst. Sediments in the horizontal caves show that, after being used by cave bears or hyenas, they were inhabited by foxes or marmots, and more recently by humans, especially during the Magdalenian period and later in the Holocene.
A prestigious Czech national monument - the medieval Charles Bridge in the historic city centre of Prague - is enclosed with sculptures carved from local sandstones. The stone exhibits varying weathering phenomena that are manifested mostly by surface blackening and local exocrust formation. Influences of the original stone composition and of atmospheric pollution on the formation of exocrust were evaluated using detailed mineralogical study and geochemistry of stable isotopes. The studied exocrusts are gypsum-dominated. Sulphur and oxygen isotope data (delta(34)S sulphate values range from +3.3 to +7.5 parts per thousand CDT with average +4.8 parts per thousand CDT from 15 measurements; delta(18)O values range from +6.4 to +9.7 parts per thousand SMOW with average +8.3 parts per thousand SMOW from 8 measurements), on sulphate, and absence of suitable sulphur source in the stone itself, strongly support anthropogenic atmospheric source of sulphur. Presence of other minor sulphates (of zinc, ammonium, magnesium, and potassium) can be explained by complex restoration and conservation treatments of the sculptures in the past. The sculptural stone - quartz sandstone derived from Cretaceous sedimentary cover of the Bohemian Massif - is deficient in both calcium and other elements forming the sulphate crusts. The results of this study show that some chemicals used for the restoration of the stone sculptures can exacerbate stone weathering especially when applied in heavily polluted urban areas.
Cryogenic cave calcite (CCC), formed by segregation of solutes during water freezing, was found in three Central European caves. This calcite type forms accumulations of loose calcite grains on cave floor. The calcite grains are of highly variable crystal morphology, and of sizes ranging from less than 1 mm to over 1 cm. The most typical feature is their accumulation as loose (uncemented) crystals. U-series dating indicates the formation of CCC in the studied caves during several climatic oscillations of the Weichselian (between 61 and 36 ka BP in the Chelsiowa Jama–Jaskinia Jaworznicka cave system in Poland, between 34 and 26 ka BP in the BUML Cave in the Czech Republic, and between 26 and 21 ka BP in the Stratenská Jaskyňa cave system, Slovakia). At the time of CCC formation, the studied caves were lying in a periglacial zone.Detailed C and O stable isotope study of CCC samples revealed that slow water freezing under isotope equilibrium was the dominant formational process in the studied Polish and Czech caves. Significantly higher δ13C values of CCC in the Stratenská Jaskyňa Cave indicate either water freezing in a more opened system with continuous CO2 escape (Rayleigh fractional separation), or participation of another CO2 source. The model of slow water freezing under isotope equilibrium is supported by isolated character of the caves having limited ventilation.In contrast, modern cryogenic cave calcite powders sampled directly on the ice surface of two recently iced caves in Slovakia with high ventilation showed much higher δ18O and δ13C data, similar to cryogenic calcites obtained in experimental rapid water freezing.
The Gemericum is a segment of the Variscan orogen subsequently deformed by the Alpine–Carpathian orogeny. The unit contains abundant siderite–sulphide and quartz–antimony veins together with stratabound siderite replacement deposits in limestones and stratiform sulphide mineralization in volcano-sedimentary sequences. The siderite–sulphide veins and siderite replacement deposits of the Gemericum represent one of the largest accumulations of siderite in the world, with about 160 million tonnes of mineable FeCO3. More than 1200 steeply dipping hydrothermal veins are arranged in a regional tectonic and compositional pattern, reflecting the distribution of regional metamorphic zones. Siderite–sulphide veins are typically contained in low-grade (chlorite zone) sedimentary, volcano-sedimentary or volcanic Lower and Upper Paleozoic rocks. Quartz–antimony veins are hosted by higher-grade units (biotite zone). Siderite–sulphide veins are dominated by early siderite followed by a complex set of stages, including quartz–sulphide (chalcopyrite, tetrahedrite), barite, tourmaline–quartz, and sulphide-remobilization stages. The temporal evolution of these stages is difficult to study because of the widespread and repeated tectonic processes, within-vein replacement and recrystallization. Siderite–sulphide veins show considerable vertical (up to 1200 m) and lateral (up to 15 km) extent, and a thickness typically reaching several metres. Carbonate-replacement siderite deposits of the Gemericum are hosted by a Silurian limestone belt and are similar to stratabound siderite deposits of the Eastern Alps (e.g., Erzberg, Austria).
The East Carpathian manganese deposits (ECMD) occur in the Tulghes Group, a Cambrian–Ordovician island arc complex metamorphosed under greenschist facies conditions during the Silurian. The deposits consist of ferromanganese carbonate–silicate orebodies (Fe-rhodochrosite, Mn-amphibole, spessartine, stilpnomelane, rhodonite, pyroxmangite and tephroite), occurring within larger and lower-grade mineralized areas. Although hosted by organic matter-rich cherts (Corg=1–1.5%), the ore is devoid of organic matter. The δ13Ccarbonate values are from −3.5‰ to −15.7‰ (PDB) in the carbonate ore and −1.7‰ to +0.9‰ in the neighboring carbonate schists, while the hosting organic matter-rich cherts exhibit δ13Corg values from −22.7‰ to −27.8‰ (PDB). The ore shows positive Ce and negative Eu anomalies on chondrite-normalized plots. The manganese was supplied by both terrigenous and igneous sources stored in oxygen-deficient bottom water of a back-arc basin and precipitated as Mn carbonate and oxide.The metamorphism of ECMD is polyphase with contrasting tendencies. The formation of silicate minerals by decarbonation reactions was followed by the extensive replacement of silicate phases by Mn carbonate and, locally, by iron sulfide, as a result of reducing fluids circulation.
Two tin–polymetallic sulfide deposits hosted by the Devonian black shale series of the Guangxi Zhuang Autonomous region occur in the Dachang ore field. The Upper Devonian (Frasnian Epoch) black shale series contains the giant Tongkeng-Changpo deposit, and the Middle Devonian (Givetian Epoch) reef limestone contains the giant Longtoushan deposit. Intrusive rocks occur at Lame and the western part of Dachang. Ores occur as stratified bodies, large veins, stockworks and zones of veinlets. Ores are massive, banded, laminated and disseminated. The ores contain more than 180 different minerals, the most important of which are cassiterite, sulfides and sulfosalts. Primary laminated sedimentary sulfide ores occur at Tongkeng. The mean ratio of SiO2/Al2O3 for shale–marl is 3.5, but values averaging 56 and 67, respectively, for ore and chert suggest a biogenic or hydrothermal source for silica. Ores and country rocks are rich in Sb, Pb, Zn, Sn and Cu; granites are rich in Sb, W, Zn and Sn. Dispersed elements, such as Te, Cd, Se and In, are abundant in ores, country rocks and granites, implying contributions of sedimentary and intrusive activities to the ore formation. Mean Y/Ho values for the black shale series (28) and granite (31) are similar to most shales and most volcanic rocks; the Y/Ho value for reef limestone is 47, comparable to sea water. Devonian black shale series are slightly LREE-enriched on chondrite-normalized plots and show small negative Eu anomalies; mean δEu (0.56),δCe (0.9) and Ceanom (−0.07) values suggest a shallow-water deposition near the redox boundary. The δ34S values of sulfides from various deposits of Dachang vary with theδ34S values for Lame ranging from −2‰ to +2‰, and values for Tongkeng-Changpo ranging from −4.9‰ to +2.6‰. The highly negativeδ34S values (−9.5‰ to −11.3‰ ) of Huile and Kengma sulfides suggest the important role of biogenic sulfur. The meanδ13C value of organic matter of Devonian black shale series is −24.6‰. Theδ30SiNBS-28 values of Upper Devonian black chert are 0.2–0.3‰, indicating a sedimentary origin. The Dachang black chert has been dated at 124±2 Ma; that of Luofu section at 387±18 Ma, implying that the Rb/Sr isotope of Dachang chert was reset during Yanshan Movement. These results suggest that the Dachang tin–polymetallic sulfide deposits exemplify strongly remobilized sedimentary mineralization.
The Dafulou and Huile vein and stratabound cassiterite-sulfide deposits and sheeted ore veins at the Kangma cassiterite-sulfide deposit are located in the eastern part of the Dachang tin field. These deposits are hosted in a sedimentary sequence containing significant concentrations of organic matter in the form of Lower Devonian calcareous black shales and hornfels. These rocks together with the younger intrusion of Longxianggai granite (91DŽ Ma) actively participated in the formation of Sn-polymetallic deposits. The following three major stages have been distinguished in stratiform and vein-type orebodies at Dafulou, Huile and Kangma: stage I (cassiterite, pyrrhotite, arsenopyrite, tourmaline, carbonate), stage II - main sulfide stage (quartz, cassiterite, arsenopyrite, pyrrhotite, sphalerite, stannite, pyrite, carbonates) and stage III (native Bi, galena, electrum, sulfosalts). Stage IV (post-ore), recognized at Huile is represented by barren carbonates and zeolites. Whole rock geochemistry has revealed that at Dafulou, Bi and Cu correlate strongly with S, whereas V and Pb correlate well with Corg (organic carbon). The similar distribution patterns of selected elements in average slightly mineralized low-Ca black shales indicate a fluid composition similar for all deposits studied. Studies of graphitization of the organic matter in black shales adjacent to orebodies indicate that d(002) and FWHM (full width in half maximum)/peak height values gradually decrease in the following sequence: Dafulou deposit M Kangma deposit M Huile deposit. The pyrolysate of wall rocks at the Dafulou deposit is relatively enriched in asphaltenes and maltenes (55.6-72.0% of the pyrolysate) comparable with pyrolysate obtained from more distal black shales (19.2-28.5%). Typical GC-MS spectra of pyrolysate from distal black shales are dominated by alkanes in the n-C15 to n-C25 range, aromatic molecules being represented mostly by alkyl-naphthalenes. In contrast, only traces of aliphatic hydrocarbons in the n-C14 to n-C18 range and elemental sulfur were identified in pyrolysates from pyrrhotitized wall rocks. The earliest fluid inclusions of the studied system occur in the quartz-tourmaline-cassiterite assemblage of stage I at Dafulou. These inclusions are H2O-CO2-CH4-rich, with 10 to 20 vol% of aqueous phase. P-T conditions of the trapping of inclusions are estimated to be up to 400 C and 1.3 to 2.0 kbar (between 5.0 and 7.5 km under lithostatic pressure). In contrast, the presence of a low density gaseous CO2-CH4 phase indicates relatively low pressures during the formation of the breccia-type quartz-calcite-cassiterite-sulfide mineralization (stage II), when P-T conditions probably reached approx. 380 to 400 C and 0.6 kbar (up to 6 km under hydrostatic pressure). Fluid inclusion data and oxygen isotope thermometry indicate that cassiterite-sulfide ores of the main sulfide stage (stage II) formed from aqueous-carbonic fluid (CO2/CH4 =&#4410) at temperatures of up to 390 C at Dafulou and in a temperature range of 250 to 360 C at Huile and 260 to 370 C at Kangma. The &#3934S values of sulfides from Dafulou range mostly between -1 and -6‰, whereas sulfides from the Kangma and Huile deposits are characterized by more negative &#3934S values (between -8 and -11‰, and between -9 and -12‰, respectively). These data suggest that bacteriogenic sulfides of black shales were a dominant source of reduced sulfur for epigenetic (vein and replacement) mineralization. Oxygen isotopic compositions of five quartz-cassiterite pairs from Dafulou and Huile show a relatively narrow range of calculated oxygen isotope temperatures (250-320 C, using the equation of Alderton 1989) and high &#3918Ofluid values between +8 and +10‰ (SMOW), which are in agreement with fluid derivation from and/or high temperature equilibration with the Longxianggai granite. The carbon and oxygen isotope composition of carbonates reflects variable carbon sources. Stage I calcite is characterized by narrow ranges of &#3913C (-7.0 to -9.5‰ PDB) and &#3918O (+15.0 to +17.5‰ SMOW). This calcite shows ubiquitous deformation, evidenced by intense development of twins. Fluid compositions calculated at 330 C for the Dafulou and Huile deposits and at 270-300 C for the Kangma deposit (&#3918Ofluid between +10.0 and +11.5‰ SMOW, &#3913Cfluid between -5.5 and -7.5‰ PDB), agree with fluid derivation from and/or equilibration with the peraluminous, high-&#3918O Longxianggai granite and suggest a significant influence of contact metasedimentary sequences (carbon derived from decomposition and/or alteration of organic matter of calcareous black shales). The ཉ C values of organic matter from the Lower to Upper Devonian host rocks at the Dafulou deposit (-24.0 and -28.0‰) fit with a marine origin from algae. However, organic matter adjacent to the host rock-ore contact displays a slight enrichment in 13C. The organic carbon from the Huile and Kangma deposits is even more 13C enriched (-24.6 to -23.5‰). The most heavy ཉ C values (-16.5‰) were detected in hornfels sampled at the contact of the Upper Devonian sediments with the Longxianggai granite. The &#3913C data broadly correlate with the degree of structural ordering (degree of graphitization) of organic matter, which indicates that both variables are related to thermal overprint.
A large number of Variscan mesothermal gold deposits are located in the central part of the Bohemian Massif, close to the Central Bohemian Plutonic Complex. The Petr&#41kova hora deposit has many features that distinguish it from other deposits in the region and suggest its mineralization is closely related to the late magmatic processes associated with the Petr&#41kova hora granodiorite. The gold ores occur as sheeted arrays of quartz veins and veinlets hosted by the small Petr&#41kova hora granodiorite stock. Gold is found mainly as free grains of >900 fineness, and is accompanied by abundant pyrrhotite and chalcopyrite, and accessory pyrite, arsenopyrite, loellingite, and molybdenite. Molybdenite from the Petr&#41kova hora deposit has been dated by the Re-Os method at 344.4&#452.8 Ma. Hydrothermal alteration in the Petr&#41kova hora deposit exhibits a distinct temporal paragenesis. Selectively pervasive, early K-alteration and silicification are the oldest hydrothermal phases. These were followed by early quartz veins (Q1 to Q4) that contain most of the gold mineralization. Late quartz veins (Q5) and fracture-controlled silicification are gold-poor or barren. Barren calcite veins are the youngest hydrothermal product. Extensive low-temperature, meteoric-water dominated alteration, as is typical of classic porphyry deposits, is absent. However, the lower &#3918O whole rock values for Petr&#41kova hora granodiorite and aplite (+2.4 to +5.1‰ SMOW) compared to other intrusions in the region reflect either interaction with isotopically light external fluids or magma assimilation of small volumes of hydrothermally altered country rock. The &#3918O isotopic compositions for quartz, scheelite and hornblende (7.7 to 13.4‰ SMOW) and the &#3934S compositions for sulfide minerals (-1 to +3.5‰ CDT) from early, gold-rich quartz veins indicate formation at high temperatures (590 to 400 C) from fluids with a magmatic isotopic signature (&#3918OFLUID of 5.7 to 7.2‰). Fluids related to late quartz veins (Q5) suggest the presence of a significant component of non-magmatic water (&#3918OFLUID: +2.5 to +4.0‰). The &#3934S values of post-Q5 sulfide minerals (-4.5 to -3.5‰) reflect at least partial derivation of late-stage sulfur from a source external to the intrusions. Aqueous, aqueous-carbonic and nitrogen-bearing fluid inclusions were identified in hydrothermal and igneous quartz, with the aqueous inclusions being the most common. In hydrothermal vein quartz, the salinity of primary aqueous inclusions falls into ranges 6 to 23 and 33 to 41 equiv. wt% NaCl; in igneous quartz, populations in salinity were observed between 5 to 16, 35 to 40 and 62 to 70 equiv. wt% NaCl. The salt component of these fluids is best, and minimally, approximated by the NaCl-KCl-CaCl2 system. Low- and high-salinity aqueous-carbonic inclusions are accessory in many of the analyzed samples. Three large successive pulses of fluids are recognized. Each pulse begins with a high-salinity (>30 equiv. wt% NaCl) magmatic fluid and evolves toward a lower salinity (~5 equiv. wt% NaCl) fluid. Data suggest that external (meteoric?) water(s) were significant for only the third fluid pulse, which formed the late Q5 quartz veins and the calcite veins. Polyphase fluid inclusions hosted by igneous quartz of the Petr&#41kova hora granodiorite indicate minimum trapping conditions of about 3 kbar and 550 C. The gold-rich Q1 to Q4 veins may have formed along a quasi-isobaric cooling path at 2.5 to 1.5 kbar and 590 to 400 C. This was followed by uplift, and formation of late Q5 quartz veins (0.5 to 1.5 kbar; ~300 C) and post-ore calcite veins (<0.5 kbar; 100 to 140 C). The characteristics of the Petr&#41kova hora deposit suggest that it may represent a position intermediate between intrusion-related gold systems (e.g., Fort Knox deposit, Alaska) and gold-rich, copper-poor porphyry deposits (e.g., Maricunga Belt in Chile). As such, the Petr&#41kova hora deposit might be an example of the reduced gold sub-type of porphyry deposit.
The Neoproterozoic volcanosedimentary sequences of the Teplá-Barrandian Unit contain several types of carbonate rocks. Most carbonate rocks are characterized by low δ13C and low δ18O values and were formed in connection with submarine volcanism and related hydrothermal activity. Significant amount of carbonate carbon of these rocks was derived from oxidation and/or pyrolysis of organic matter. In the Příbram area rare oolitic carbonate lenses were found with high δ13C values up to +6 ‰ corresponding to the typical isotopic composition of Neoproterozoic limestones of the world. Oxygen isotope data of oolitic limestones of the Příbram area and of adjacent rocks, chert with intercalated dolomitic limestone, indicate that the formation of the studied rocks was also related to submarine hydrothermal activity. Abundant H2S-rich fluid inclusions characteristic of diagenetic environment support the idea that the isotope data reflect original depositional conditions with only minor alterations during later weak regional metamorphism. In the Mitov-Kokšín area the fluid inclusion study indicates a much higher pressure characteristic of subsea-floor metamorphism. Oxygen isotope data of several chert types are in the range between +16.6 and +21.1 ‰ (SMOW). Within this range the δ18O data for stromatolite-like cherts are the highest, indicating lower temperature of formation while dark-coloured bedded cherts (lydites) and light-coloured cherts were formed at a higher temperature. Individual growth, zones of siliceous stromatolitic structures showed almost identical δ18O data.
The late Variscan (275-278 Ma) Pribram uranium deposit is one of the largest known accumulations of uraniferous bitumens in hydrothermal veins. The deposit extends along the northwestern boundary of the Central Bohemian pluton (345-335 Ma) with low-grade metamorphosed Late Proterozoic and unmetamorphosed Cambrian rocks. From a net uranium production of 41,742 metric tons (t), more than 6,000 t were extracted from bitumen-uraninite ores during 43 years of exploration and mining. Three morphological varieties of solid bitumen are recognized: globular, asphaltlike, and cokelike. While the globular bitumen is uranium free, the other two types are uraniferous. The amount of bitumen in ore veins gradually decreases toward the contact with the plutonic body and increases with depth. Two types of bitumen microtextures are recognized using high-resolution transmission electron microscopy: amorphous and microporous, the former being less common in uraniferous samples. A lower Raman peak area ratio (1,360/1,575 cm-1) in mineralized bitumens (0.9) compared with uranium-free samples (2.0) indicates a lower degree of microtextural organization in the latter. The H/C and O/C atomic ratios in uranium-free bitumens (0.9-1.1 and 0.09, respectively) are higher than those in mineralized samples (H/C = 0.3-0.8, O/C = 0.03-0.09). The chloroform extractable matter yield is very low in uranium-free bitumens (0.30-0.35% of the total organic carbon, TOC) and decreases with uranium content increase. The extracted solid uraniferous bitumen infrared spectra show depletion in aliphatic CH2 and CH3 groups compared to uranium-free samples. The concentration of oxygen-bearing functional groups relative to aromatic bonds in the IR spectra of uranium-free and mineralized bitumen, however, do not differ significantly. 13C NMR confirmed than the aromaticity of a uraniferous sample is higher (F(ar) = 0.61) than in the uranium-free bitumen (F(ar) = 0.51). Pyrolysates from uraniferous and nonuraniferous bitumens do not differ significantly, being predominantly cresol, alkylphenols, alkylbenzenes, and alkylnaphthalenes. The liquid pyrolysate yield decreases significantly with increasing uranium content. The δ13C values of bulk uranium-free bitumens and low-grade uraniferous, asphaltlike bitumens range from -43.6 to -52.3 per mil. High-grade, cokelike, uraniferous bitumens are more 13C depleted (-54.5 to -58.4‰). In contrast to the very light isotopic ratios of the high-grade uraniferous cokelike bitumen bulk carbon, the individual n-alkanes and isoprenoids (pristane and phytane) extracted from the same sample are significantly 13C enriched. The isotopic composition of the C13-24 n-alkanes extracted from the high-grade uraniferous sample (δ13C = -28.0 to -32.6‰) are heavier compared with the same compounds in a uranium-free sample (δ13C = -31.9 to -33.8‰). It is proposed that the bitumen source was the isotopically light (δ13C = -35.8 to -30.2‰) organic matter of the Upper Proterozoic host rocks that were pyrolyzed during intrusion of the Central Bohemian pluton. The 13C-depleted pyrolysates were mobilized from the innermost part of the contact-metamorphic aureole, accumulated in structural traps in less thermally influenced parts of the sedimentary complex and were later extracted by hydrothermal fluids. Bitumens at the Pribram deposit are younger than the main part of the uranium mineralization and were formed through water-washing and radiation-induced polymerization of both the gaseous and liquid pyrolysates. Direct evidence for pyrolysate reduction of uranium in the hydrothermal system is difficult to obtain as the chemical composition of the original organic fluid phase was modified during water-washing and radiolytic alteration. However, indirect evidence-e.g., higher O/C atomic ratios in uranium-free bitumens (0.1) relative to the Upper Proterozoic source rocks (0.02-0.05), isotopically very light carbon in associated whewellite (δ13C = -31.7 to -28.4‰), and the striking absence of bitumens in the pre-uranium, hematite stage of the mineralization-indicates that oxidation of organic fluids may have contributed to lowering of aO2 and uraninite precipitation.
The abandoned Roztoky silver-based metal deposit represents a scarce example of Tertiary sulphide vein-type mineralization spatially and genetically associated with intraplate volcanic rocks of the Cenozoic West and Central European Volcanic Province. The deposit is situated in the Tertiary Roztoky Volcanic Centre (RVC) of the Ceske stredohori Mts., within the Ohre (Eger) Rift. The main ore vein parallels an older bostonite dyke intersecting the monzodiorite body, however, both are intersected by a younger trachyte dike. This suggests that the origin of the mineralization is related to the development of the RVC. The δ13C values of vein carbonates indicate the influence of deep-seated CO2 but the O isotopic composition of hydrothermal fluids (calculated δ18Ofluid values from -3 to -7‰ SNOW) shows the dominance of water with relatively shallow circulation. Sphalerite-galena sulphur isotopic geothermometry yielded temperatures between 200 and 250°C and the presence of cubic hessite indicates temperatures above 155°C. The calculated δ34Sfluid values vary in the range -1.0 to -2.0‰. The presence of banded 'colloform' sphalerite and chalcedony suggests lower temperatures. High lead isotope ratios of galena (206Pb/204Pb about 19.03, 207Pb/204Pb about 15.67, 208Pb/204Pb about 39.17) can be a result of mobilization of lead either from Tertiary magmatic rocks, which show similar lead isotope ratios and were probably derived from a sublithospheric HIMU mantle source, or from upper-crustal rocks, e.g. local Upper Cretaceous sediments. The 87Sr/86Sr isotope ratios of the principal hydrothermal carbonates rhodochrosite (0.70524) and calcite-dolomite (0.70510) are higher than both the local primitive magma derivatives and even the developed rocks of the RVC and indicate an admixture of Sr derived from local crustal rocks. The volcanic rocks of the RVC were the dominant heat source during the formation of the ore deposit. The hydrothermal deposit was formed during relatively shallow hydrothermal circulation of low to medium salinity, low-δ18O fluids supported by CO2 influx of deep-seated origin.
Variscan Au-mineralization in the central part of the Bohemian Massif belongs to mesothermal type with the exception of Petráčkova hora deposit (porphyry-gold type). Early minerals (quartz of early stages etc.) in mesothermal deposits crystallized from H2O > CO ± CH4 ± N2 low-salinity fluids. Their isotope composition (C, O, S) was controlled by equilibration with surrounding metamorphic and magmatic rocks at higher temperatures. Gold precipitation was related to H2O or H2O-CO2 fluids with temperatures usually in the range 300 to 200°C. Their O-isotope composition indicates increasing amount of isotopically lighter fluids (meteoric component ?) in later stages. Early mineralization stages of Petráčkova hora porphyry-gold deposit are related to high-salinity aqueous magmatic fluids which mixed with low-salinity, high-temperature external fluids. Quartz precipitated at 550 to 400°C, gold at around 400°C. Isotope composition (O, S) of early fluids was in equilibrium with granitoid rocks/magma.
Extensive calcite-rich replacements after wollastonite have been found in an abandoned marble quarry near Nezdice, Šumava Mrs., southern Czech Republic. Because any natural reversals of wollastonite reaction both in high-temperature and low-temperature environment are rare, combined mineralogical and stable isotope study of these pseudomorphs was performed. Other types of calcite observed in the quarry include marble in the zones of metamorphic decarbonation, hydrothermal vein calcite and calcite related to karstification process. Stable isotope and fluid inclusion methods were used to study the other types of calcite for comparison purposes. A plausible scenario of the formation of the calcite pseudomorphs involves the following two step evolution mode: (1) transformation of wollastonite to optically and X-ray amorphose phase (which could probably result from a high-rate tectonic deformation or shock wave compression), (2) reaction of the relatively unstable amorphose phase with water having high contents of CO2 to CaCO3, mainly in the zone of supergene alteration. Formation of the secondary carbonates during weathering is strongly indicated by oxygen and carbon isotope composition. The carbonate-rich pseudomorphs after wollastonite still contain relics of the optically and X-ray amorphose phase which formed by transformation of wollastonite and retains its accicular crystal shape. Alternative modes of formation of the pseudomorphs, including, e.g., a spontaneous decomposition of wollastonite to CaO + SiO2 (due to shock wave deformation) during the step (1) or high-temperature reaction of a part of wollastonite with calcite (from the enclosing marble) to larnite, spurrite, or other very high-temperature minerals (also an alternative of step 1) could not be supported by observation; no remains of CaO or larnite were observed. Such unstable high-temparature minerals formed from wollastonite would transform to CaCO3-rich pseudomorphs on exposure to water having a high content of CO2. Formation of the pseudomorphs by incongruent dissolution of wollastonite in the zone of weathering is not supported by observation - wollastonite behaviour as a stable mineral during weathering is well known. Associated diopside, quartz, and primary calcite show no replacement by secondary calcite. Stable isotope analyses and fluid inclusion study of calcite crystals coating some open fractures in the marble quarry indicate that this hydrothermal acivity has no connection with formation of the pseudomorphs after wollastonite.
Strata-bound harite-hyalophane sulfidic orebodies recently discovered at Rožná (in the Moldanubian zone of the Bohemian Massif, Czech Republic) are hosted within the high-grade metamorphosed complex composed of migmatitic biotite or sillimanite-biotite gneiss and amphibolite, with rare intercalations of marble and calcsilicate gneiss. The orebodies and the host rocks have a complex metamorphic history. The last Variscan amphibolite facies metamorphic event is recorded in the quartz-biotite oxygen isotope fractionation in the host gneiss, which indicates temperatures from 600° to 700°C. Metamorphic textures in the orebodies include granoblastic annealing-recrystallization of barite and sulfides, pressure solution seams, and local development of shear zones near the margins of the orebodies. Despite intense metamorphism, the ore is generally strata bound, with sharp host-rock contacts. At a few places, tectonically modified offsets (usually enriched in sulfides) extend up to 2 m across the foliation of the surrounding rocks. Based on ore mineralogy and texture, the orebodies can be divided into three types: (1) massive barite-hyalophane sulfidic rock, (2) calc-silicate gneiss with minor barite and sulfides, and (3) disseminated sulfides in marble. Massive barite ore, which is the only type of mineralization of economic interest (with estimated reserves of over 2 million tons [Mt]), contains an average of 62.2 percent barite, 3.2 percent Zn, and 1.8 percent Pb. The relatively simple mineral assemblage of massive ore includes barite, hyalophane, calcite, quartz, pyrite, pyrrhotite, sphalerite, and galena, as well as minor amounts of pyrargyrite, Ag tetrahedrite, fluorite, pyrophanite, and ilmenite. Calc-silicate gneiss with sulfides and barite usually forms the outer parts of the barite orebodies hosted in gneiss. It consists mainly of pyroxene, hyalophane, and quartz, with minor garnet, calcite, forsterite, minerals of the zoisite group, and sulfides. Disseminated Pb-Zn mineralization in marbles occurs only near the contact of marbles with massive barite orebodies. The δ 34S values of sulfide minerals are heavy in all mineralization types (7.2-14.8 ‰), probably indicating their formation in an anoxic, restricted marine environment, where the isotopic composition of sulfate and sulfide gradually shifted to more positive values as a result of the fractionation of S isotopes during bacterial reduction of sulfate to sulfide and the removal of isotopically light S by sulfide sedimentation. The restricted character of the sedimentary environment during barite formation is supported by the elevated content of graphite in the host rocks (0.01-2.0%) and by very heavy δ 34S values of pyrite and anhydrite in a small (up to 1 m thick) anhydrite lens that occurs in a host-rock complex. The 87Sr/ 86Sr ratios in barite ore (0.7077-0.7079) are close to those for anhydrite (0.7080). Because the anhydrite probably represents a meta-evaporite, the isotopic composition of both barite and anhydrite strontium is close to that of contemporaneous seawater. The isotopic composition of lead in galenas from massive barite and calc-silicate ore is very homogeneous ( 206Pb/ 204Pb from 17.65 to 17.66, 207Pb/ 204Pb from 5.47 to 15.51, and 208Pb/ 204Pb from 37.36 to 37.45), and lead isotope ratios prove the pre-Variscan age of the orebodies. It is proposed that the Rožná strata-bound mineralization formed by mixing of the hydrothermal solutions carrying Ba, Zn, and Pb with seawater in a restricted oceanic or intra-arc trough filled with clastic sediments derived mostly from contemporaneous volcanic rocks. The restricted nature of the trough resulted in low oxygen contents in the bottom waters and low recycling rates for the organic matter. During the subsequent thermal events, the mineralization and its host rocks were deformed and metamorphosed to the upper amphibolite grade and the carbonate-enriched orebodies were transformed to calc-silicate ore. Following deformation and retrograde metamorphic events at rather superficial tectonic levels caused retrograde shearing at the margins of the orebodies. At a waning stage of the metamorphism, the ore and host rocks were metamorphosed under greenschist facies conditions.
Dykes of alkaline and ultramafic carbonate lamprophyres (monchiquite-ouachitite and aillikite) intrude the Carboniferous sediments of Central Bohemia. Their characteristic feature is the presence of substantial amounts of a sodalite group mineral (presumably haüyne), carbonate and barite. Isotopic compositions ofδ 13C (−3.4 to −6.2‰) andδ 18O ( + 13.5 to + 15.9‰) indicate that the carbonate is of primary magmatic origin and that fluids were formed at temperatures of 500 to 350°C. High contents of CO2 (3.6 to 17.6 wt.%) and incompatible elements, high LREE/HREE ratios (30.0 to 57.7), and low Rb/Sr (0.025 to 0.078) and87Sr/86Sr (0.7038 to 0.7042) ratios suggest the ultramafic lamprophyres are related to deep-seated carbonated magmas of mantle origin. Low degree of partial melting ( < 1%) of the mantle peridotite is envisaged, with additional transport of fluids rich in incompatible elements into the crustal chamber. Alkaline lamprophyres are fractionated derivatives which originated from the same source. Magma intrusion from different levels of a magma chamber into fracture zones under horizontal tension without a central intrusion could result in variability in lamprophyre composition (cumulates or evolved derivatives).
Jednotlivé sv. mají ISBN Od roč. 25. podnázev: sborník pro regionální výzkum Od roč. 34 podnázev: časopis pro regionální výzkum = bulletin for regional research Od roč. 19.: Uspořádali Irena Jančaříková, Pavel Bosák Od roč. 34.: Uspořádali Pavel Bosák a Karel Žák Od roč. 19. nakl.: Beroun, Muzeum Českého krasu

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Roman Skala
  • Institute of Geology, Academy of Sciences of the Czech Republic, Prague, Cech Republic
Helena Hercman
  • Polish Academy of Sciences
Lukáš Ackerman
  • The Czech Academy of Sciences
Jan Pašava
  • Czech Geological Survey
Sarka Krizova Jonasova
  • The Czech Academy of Sciences
Bogdan P. Onac
  • University of South Florida
Jiri Mizera
  • The Czech Academy of Sciences

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The Czech Academy of Sciences
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  • Institute of Geology
Ruhr-Universität Bochum
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  • Institute of Geology, Geophysics and Mineralogy

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