Walter Prochaska

Origin of siderite veins in the Western Carpathians: I. P–T–X–δ13C–δ18O relations in ore-forming brines of the Rudňany deposits

Abstract Siderite–barite veins of the Rudňany ore field have precipitated from NaCl–CaCl 2 –H 2 O±CO 2 solutions with CaCl 2 weight fractions between 0.05 and 0.38, total salinities between 17 and 35 wt.%, and up to 1.8 mol% CO 2 . Homogeneous and heterogeneous trapping modes have been distinguished according to volumetric phase ratios of the fluid inclusions, which have been trapped at 175–205 °C in veiny siderite, at 200–230 °C in siderite and quartz from drusy cavities, and at 90–180 °C in the siderite–postdating quartz–sulfidic assemblage. A sequential re-equilibration technique has been developed to locate precisely vapour-saturated halite liquidus of individual brine inclusions, which normally homogenise by halite dissolution. Slopes of the vapour-unsaturated halite liquidi constrained by isochores of coexisting two-phase aqueous inclusions have been approximately three to five times steeper in natural polycomponent brines than those in the experimental NaCl–H 2 O system. Fluid pressures between 1 and 2 kbar have been determined using this method in drusy quartz, associating with siderite crystals. Oxygen isotope variations (16.8–19.9‰ V-SMOW) in siderite result from a temperature increase from ∼175 to ∼230 °C, whereas nearly constant δ 13 C values (−3.9‰ to −4.6‰ V-PDB) indicate absence of CO 2 devolatilisation. Carbon isotope composition of the parental fluid changed from −9.5‰ to −8.8‰ V-PDB, while the oxygen isotope ratios remained essentially fixed at 7.7±0.3‰ V-SMOV during formation of siderite. The calculated δ 18 O fluid value is attributed to formation water enriched in 18 O during isotopic exchange with crustal rocks at low fluid/rock ratios. The δ 13 C fluid values probably correspond to a mixture of CO 2 from dissolved matrix carbonates and that liberated by thermal decarboxylation of organic acids (acetates), which normally occur in formation waters. Leachate chemistry data have corroborated high concentrations of CaCl 2 and MgCl 2 in the ore-forming brines. High Br concentrations are similar to halite-fractionated basinal brines. Ca 2+ and K + concentrations in excess of those in normal basinal brines reflect extensive cation exchange with surrounding low- to medium-grade metamorphites, coincidental with calcite and K-feldspar dissolution, dolomitisation, and albitisation of plagioclases. High pressures of the siderite-forming fluids (1–2 kbar) must be linked with a deep circulation (∼4–8 km) of the basinal brines derived primarily from marine water, but significantly modified by interaction with low- to medium-grade Paleozoic rocks at low fluid-to-rock ratios. An anti-clockwise crystallisation PT path inferred from fluid inclusion and stable isotope data is inconsistent with the siderite precipitation during extensional tectonic regime coincidental with Permian–Triassic rifting suggested in previous models. More likely, the progressively increasing fluid pressures and temperatures could be attributed to compression and crustal thickening triggered by Jurassic subduction in the Meliatic–Hallstatt oceanic suture. The superimposed quartz–ankerite–sulfidic ores have likely crystallised from brines expelled during compression associated with a continental collision during Early to Middle Cretaceous times.

Cathodoluminescence, fluid inclusion and stable C–O isotope study of tectonic breccias from thrusting plane of a thin-skinned calcareous nappe

Basal hydraulic breccias of alpine thin-skinned Muráň nappe were investigated by means of cathodoluminescence petrography, stable isotope geochemistry and fluid inclusions analysis. Our study reveals an unusual dynamic fluid regime along basal thrust plane during final episode of the nappe emplacement over its metamorphic substratum. Basal thrusting fluids enriched in 18O, silica, alumina, alkalies and phosphates were generated in the underlying metamorphosed basement at epizonal conditions corresponding to the temperatures of 400–450°C. The fluids fluxed the tectonized nappe base, leached evaporite-bearing formations in hangingwall, whereby becoming oversaturated with sulphates and chlorides. The fluids further modified their composition by dedolomitization and isotopic exchange with the host carbonatic cataclasites. Newly formed mineral assemblage of quartz, phlogopite, albite, potassium feldspar, apatite, dravite tourmaline and anhydrite precipitated from these fluids on cooling down to 180–200°C. Finally, the cataclastic mush was cemented by calcite at ambient anchizonal conditions. Recurrent fluid injections as described above probably enhanced the final motion of the Muráň nappe.

Aphrodisian marble from the Göktepe quarries: the Little Barbarians, Roman copies from the Attalid Dedication in Athens

The marble of seven under-lifesize sculptures of barbarians, now in the archaeological museums of Naples, Venice and the Vatican, commonly considered to be Roman copies of the Pergamene Lesser Dedication in Athens, comes from the Goktepe marble quarries near Aphrodisias, as is shown by isotopic, electron paramagnetic resonance, trace analyses, and of petrographic data. Since this marble was used mostly by Aphrodisian artists, this finding confirms, on the basis of scientific data, previous hypotheses on the origin of the sculptors who manufactured the statues. Reliable discrimination from similar fine-grained Asiatic marbles, such as Docimium , is possible primarily on the basis of the composition of the Goktepe marbles, which have unusually low concentrations of manganese and high concentrations of strontium. Present knowledge of the history of the quarries and the distribution of their marbles seems to rule out the possibility that the sculptures date from the late Republican period and supports the opinion, previously proposed on stylistic grounds, that they were manufactured in Rome by Aphrodisian sculptors probably during the first half of the second century ad .

The metamorphosed molybdenum vein-type deposit of the Alpeinerscharte, Tyrol (Austria) and its relation to Variscan granitoids

The molybdenite deposit of the Alpeinerscharte (Austria) is situated in Variscan greenschist- to amphibolite-facies metamorphosed granodiorites and granites of the western Tauern Window. These granitoids represent strongly fractionated calc-alkaline I-type magmas with minor S-type components and reveal post-orogenic affinities. Molybdenum contents (average 4.3 ppm) are slightly above the general background of average granites. Molybdenite mineralization is restricted to narrow quartz veins and quartz vein selvages which are presently composed of biotite and (almandine-grossular) garnet. These selvages show geochemical features typical of intermediate argillic alteration in a hydrothermal system postdating granite intrusion: instability of plagioclase causes removal of Na, Ba, Sr, Pb and Eu, while K and Ca remain nearly constant. Rare earth elements (apart from Eu) and metals are extremely enriched. Application of Fe-Mg exchange (garnet-biotite) and oxygen isotope (quartz-garnet, quartz-plagioclase) geothermometers to vein selvage mineral assemblages reveals temperatures of the late-Alpine (35–55 Ma) metamorphic overprint (∼540°C, 7–10 kbar). Leucocratic rocks composed of mainly orthoclase and plagioclase are occasionally spatially related to molybdenite-bearing veins; they are interpreted as episyenites formed by hydrothermal alteration of the host granite. This episyenitic alteration is characterized by a mass loss of ca. 30%, relative enrichment of plagioclase components, extreme depletion of Si, and minor depletion of Fe, Zn, Cu and Mo.

Bronze Age höyüks, Iron Age hilltop forts, Roman poleis and Byzantine pilgrimage in Germia and its vicinity. ‘Connectivity’ and a lack of ‘definite places’ on the central Anatolian high plateau

Abstract Germia was a well-connected Byzantine polis in western-central Anatolia, famous for its healing waters and a church of St Michael. After three years of survey the site can now be reconstructed: it included several other churches and monasteries, but little space for ordinary residential buildings. This comes as a surprise, but can be explained by the discovery of two older Roman cities within walking-distance of Germia, where the ordinary people seem to have lived. One of these cities, Mantalos, was home to a local cult of the pagan god Men. This may explain why the Christian healing centre was established at Germia. Later, Mantalos shed its pagan legacy and was apparently renamed Eudoxias after a homonymous member of the Theodosian dynasty. No Roman or Byzantine settlement of the region has a history extending back beyond the Iron Age, when the population retreated to fortified hilltop settlements and many sizable Bronze Age höyüks were deserted. Settlement locations changed often and grew little in central Anatolia, and this may be blamed on the uniform landscape of the high plateau; it lacks the Mediterraneans diverse geography of ‘definite places’ that would favour one site above others and ensure its continuity and growth. Özet İç Batı Anadolu’da yer alan Germia, şifalı suları ve St Michael’a ait kilisesi ile ünlü ve iyi bağlantılara sahip bir Bizans şehridir. Üç yıl süren yüzey araştırması sonrasında yerleşim rekonstrükte edilebilmiştir. Birçok kilise ve manastırlara sahiptir; fakat olağan konutsal yapılar için az alan bulunmaktadır. Bu durum şaşırtıcı olsa da, Germia’ya yürüme mesafesinde yer alan ve olasılıkla sıradan insanların yaşamış olduğu, iki daha eski Roma şehrinin varlığıyla açıklanabilir. Bu şehirlerden biri olan Mantalos, pagan tanrısı Men’e ait yerel külte ev sahipliği yapmaktaydı. Bu durum, Hıristiyan şifa merkezinin neden Germia’da yapıldığını açıklayabilir. Sonradan, Mantalos pagan mirasından sıyrılmış ve anlaşılan Theodosius hanedanlığından bir kişiyle aynı ismi alarak Eudoxias olarak yeniden adlandırılmıştır. Bölgedeki hiçbir Roma ve Bizans yerleşiminin Demir Çağı’ndan öncesine uzanan bir geçmişi saptanamamıştır. Bunun nedeni toplumun tepe üzerinde yer alan tahkimli yerleşimlere geri çekilişiyle pek çok büyük Tunç Çağı höyüklerinin terkedilmiş olmasıdır. Orta Anadolu’da yerleşim yerleri sıklıkla değişmiştir ve çok az büyüme göstermiştir. Bu durum yüksek platonun tek düzey yüzey şekli ile açıklanabilir. Bu bölge, Akdeniz’in çeşitlilik gösteren coğrafyasında yer alan, bir yerleşimi diğerlerinden ayrıcalıklı yapan ve devamlılığı sayesinde büyümeyi sağlayan belirli özelliklere sahip ‘sınırlı bölgeler’den yoksundur.

Palaeofluid flow in siliciclastic Lower Carboniferous rocks: Evidence from stable isotopes and fluid inclusions, Rhenohercynian Zone, Czech Republic

Post-Variscan Zn, Pb, Cu vein minera-lisation occurs within the Lower Carboniferous siliciclastic rocks at the eastern border of the Bohemian Massif. Saddle dolomites are associated with this vein mineralisation and indicate a NW-SE oriented fluid flow through the Palaeozoic rocks. The major control on this fluid flow pattern is experted by faults. Eutectic temperature and crush-leach analyses indicate H2O-NaCl-CaCl2 type of basinal brines. Homogenization temperatures regionally decrease from 147° to 80°C and salinities from 26.5 to 17 wt.% eq. NaCl. Temperatures correlate well with an increase of_δ18O values from 15.5 to 22.5%. SMOW and_δ13C values from_−5.6 to_−3.1%. PDB.

Innovative application of portable X-ray fluorescence (XRF) to identify Göktepe white marble artifacts

An efficient and non-destructive method to classify white marble artifacts by using a hand-held, portable XRF analyzer (pXRF) is here reported. The identification is based on the uniquely high strontium content of this marble and has been verified by testing 32 artifacts, most of which had already been provenanced, using conventional micro-destructive analyses. Besides strontium, other potential provenance indicators, such as manganese and iron, were analyzed and their concentration values obtained after empirical calibration of the instrument by using 17 quarry samples of known composition. The results show that Göktepe/non-Göktepe discrimination is almost always possible (30 artifacts) and that additional analyses are required only when the Sr value is at the lower edge of the Göktepe field (2 artifacts). The success of the method, however, resides in the particular composition relative to trace elements of Göktepe and is not easily extended to other marble varieties. Main reasons are related to insufficient accuracy at low concentration values, intrinsic trace variability of marble artifacts, surface effects that may produce not representative results. Interest in the method therefore is tightly linked to the exceptional importance of Göktepe as a sculptural marble, in which case, detailed data, obtained with a fast and totally non-destructive method, may provide relevant information concerning chronology, workshops, and places of production of the artifacts.

Light Hydrocarbon Geochemistry of Oils in the Alpine Foreland Basin: Impact of Geothermal Fluids on the Petroleum System

Oil is produced in the Austrian sector of the Alpine Foreland Basin from Eocene and Cenomanian reservoirs. Apart from petroleum, the basin hosts a significant geothermal potential, which is based on the regional flow of meteoric water through Malmian (Upper Jurassic) carbonate rocks. Oils are predominantly composed of n-alkanes, while some samples are progressively depleted in light aromatic components. The depletion in aromatic components relative to abundant n-alkanes is an effect of water washing. Waters coproduced with oils that are affected by water washing show a progressive reduction in salinity and depletion in 2H and 18O isotopes, indicating that the degree of water washing is mainly controlled by the inflow of meteoric water from the Malmian aquifer. In some fields with Cenomanian reservoir rocks, a hydraulic connectivity with the Malmian aquifer is evident. However, water washing is also recognized in Eocene reservoirs and in areas where the Malmian aquifer is missing. This shows that existing flow models for the regional Malmian aquifer have to be modified. Therefore, the results emphasize the importance of combining data from the petroleum and geothermal industry, which are often handled separately.

Genetic concepts on the formation of the Austrian magnesite and siderite mineralizations in the Eastern Alps of Austria

A consanguineous origin of the sparry siderite and magnesite mineralizations of the Eastern Alps has been repeatedly discussed in the past, often without the back-up of sound scientificarguments. Here, it is shown that the characteristics of these mineralizations including structures, fluid parameters, timing etc. are amazingly similar suggesting in fact the genetic linkage of these deposits. The siderite as well as the magnesite mineralizations of the Eastern Alps exhibit metasomatic-epigenetic structures of lens-shaped orebodies with dolomitic alteration rims as dominant features. The basic chemical characteristics of the ore forming fluids in these mineralizations are those of highly fractionated hypersaline fluids exhibiting all the features of residual bittern brines. Fluid invasion and mineralization structures strictly depend on the original lithology of the host rocks, mainly carbonatic sedimentary rocks. In Late Triassic times, these buried evaporitic brines were mobilized either by magmatic/metamorphic processes in the underlying crystalline units or by the superimposed sedimentary upload of the Triassic platform carbonates thus leading to magnesite formation. Initially these residual, bittern brineswere completely free of Fe and rich in Mg suitable for the formation of magnesite. Deeperand more extensive circulation of these fluids and their interaction with the host-rock, resulted in the uptake of Fe and the formation of siderite.

Permian–polysulphide-siderite–barite–haematite deposit Rude in Samoborska Gora Mts., Zagorje–Transdanubian zone of the Inner Dinarides

Samoborska Gora Mts. is situated within the westernmost part of the Zagorje–Mid–Transdanubian zone of the Internal Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralisation is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralisation, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulphide–barite–quartz veins are located below the stratabound mineralisation. The stratiform part ofthe deposit is situated above the stratabound and consists of haematite layer with barite concretions and veinlets. Late stage galena–barite veins overprint earlier types of mineralisation. The Rude ore deposit was generated by predominantly NaCl±CaCl 2 –H 2 O solutions. Detrital quartz from stratiform mineralisation contains fluid inclusions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150°C to 230°C. Stratabound/siderite–polysulphide–barite–quartz vein type mineralisation was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 60°C and 160°C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100°C to 140 °C. Fluid inclusion bulk leachate chemistry recorded Na + >Mg 2+ >K + >Ca 2+ >Li + and Cl - >SO 4 2- ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br - content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulphate. Ore–forming fl uids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite–polysulphide–barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje–Mid–Transdanubian Zone and the Gemerides, and southeastward to the Hellenide–Albanides.