Walter Prochaska | Montanuniversität Leoben (original) (raw)

Papers by Walter Prochaska

Archäologischer Anzeiger, 2013

Throughout antiquity the landlocked highlands of northern Macedonia employed various local and im... more Throughout antiquity the landlocked highlands of northern Macedonia employed various local and imported marbles. Among them a certain fine-grained white dolomite stands out both in number of artefacts and in quality of workmanship. The material was used for Roman sculptures as well as the best carvings from Late Antiquity and can be traced back to an ancient quarry at Sivec near Prilep. Local workshops must have been based there or at nearby cities. This contrasts with the southern lowlands south of the Demir Kapija Gorge, where Thasian marble appears the default white marble preference and could be imported with relative ease via the Axios/Vardar River. In Late Antiquity, Sivec marble started to be carved in a style and quality that is without precedent in the region, but often indistinguishable from the production of the quarries and workshops at Proconnesus/Constantinople and Docimium in Anatolia. The three Late Antique quarries seem to have been interconnected in a way that is reminiscent of and possibly in part based on the Roman quarry system.

Journal of Geochemical Exploration, 2009

Rare earth elements and yttrium geochemistry of dolomite from post-Variscan vein-type Zn–Pb–Cu mi... more Rare earth elements and yttrium geochemistry of dolomite from post-Variscan vein-type Zn–Pb–Cu mineralization was studied in the Nízký Jeseník and Upper Silesian Basins. Combined with crush–leach analyses of fluid inclusions, the study provided important information on fluid–rock interaction, physico-chemical and redox conditions during crystallization of the dolomite. The mineralization is hosted by Carboniferous siliciclastic rocks, representing Variscan flysch and molasse sedimentation. Dolomite samples contain highly variable contents of REE (between 18 and 295 ppm) and Y (between 17 and 95 ppm). REY patterns are divided into four different groups which differ in regional provenance, LREE vs. HREE enrichment/depletion and significance of Eu, Gd and Y anomalies. These patterns can be the result of 1) precipitation of dolomite from near neutral fluids with important concentrations of complexing ligands as a main factor for the REY partitioning, 2) interaction of migrating fluids with host or basement rocks, or, most probably, 3) a combination of both.Regarding the importance of complexing ligands, it is proposed that in all samples fluoride and chloride complexes prevailed over sulphate, bicarbonate and hydroxide complexes. Interaction of fluids with rocks was strongly affected by the fluid temperature. Dolomites which precipitated from fluids with homogenization temperature higher than 110 °C are mostly REY-enriched while fluids colder than 110 °C produced REY-depleted dolomite. The REY-enrichment may indicate higher effectiveness of leaching of REE-bearing minerals (probably monazite, allanite and biotite) at higher temperatures. The preferential loss of LREE can be caused by the recrystallization or remobilization of dolomite. Generally, an increase in salinity and contents of Cl and F in the fluids is mostly accompanied by a higher REY content in dolomite. Positive Eu anomalies and small negative Gd and Y anomalies are typical for most of the chondrite-normalized patterns. Positive EuCN anomalies in dolomites are most probably the result of an increase of Eh in the parent fluid. Distribution of Y is expected to be predominantly controlled by solution complexation.

Doklady Earth Sciences, 2009

The deposits of crystalline magnesite in the carbonate sequences are the main economic genetic ty... more The deposits of crystalline magnesite in the carbonate sequences are the main economic genetic type for obtaining metallurgical refractory material. Their genesis is actively debated in the geological literature. The magnesite deposits of the Southern Urals Province are the main, intensely mined magnesite deposits of Russia. There are different viewpoints regarding the source of magnesium in them and their formation mechanism. The main hypotheses are sedimentogenic (magnesium was removed from the weathering crust after basic rocks and precipitated in the coastal-marine carbonate basins [1]), hydrothermal-metasomatic (magnesium was supplied with postmagmatic or metamorphogenic fluids, which then formed metasomatic lodes [2, 3]), elision-catagenetic (finely dispersed magnesite was formed in the evaporite carbonate lagoons, and then redistributed in metasomatic ore bodies by elision-catagenetic fluids [4]). The same hypotheses (sedimentary and hydrothermal-metasomatic) were proposed for geologically similar deposits of crystalline magnesite in Austria and Slovakia known as Veitsch type-deposits . At the same type, data obtained on Cl-Br-Na systematics of fluid inclusions in magnesites of Veitschtype deposits indicate the evaporite nature of high-Mg ore-bearing fluids . These brines presumably formed metasomatic lodes of crystalline magnesite in the Paleozoic sequences under extensional conditions existing in the Permian and Triassic. The study of Cl-Br-Na systematics of fluid inclusions in the magnesites of the Satka subtype of the Southern Urals magnesite province also revealed their evaporite nature . However, since the province contains deposits of several subtypes that differ in geological conditions and ore quality, we studied the fluid inclusions in other typical deposits. These investigations showed that fluid inclusions in other deposits also have an evaporite origin, and, hence, evaporitic brines were the main sources for magnesian fluids during formation of crystalline magnesite deposits of the Southern Urals magnesite province.

Die Forschungsfelder liegen umfassend im Bereich der mineralischen Rohstoffe und ihrer Lagerstätt... more Die Forschungsfelder liegen umfassend im Bereich der mineralischen Rohstoffe und ihrer Lagerstätten. Die Lehre konzentriert sich in den Bakkalaureat- und Magisterprogrammen der Studienrichtungen Angewandte Geowissenschaften, Natural Resources und Petroleum Engineering auf die Grundlagen der Geologie, Lagerstättenkunde und Montangeologie. Research is focused on various aspects of mineral resources and their deposits. The courses offered for the bachelor and magister programmes in Applied Geosciences, Natural Resources and Petroleum Engineering cover a broad field of geological basics, deposit prospecting and mining geology.

Ore Geology Reviews, 2011

Pb–Zn–Ag vein and listwaenite types of mineralization in Crnac deposit, Western Vardar zone, were... more Pb–Zn–Ag vein and listwaenite types of mineralization in Crnac deposit, Western Vardar zone, were deposited within several stages: (i) the pre-ore stage comprises pyrite, arsenopyrite, pyrrhotite, quartz, kaolinite and is followed by magnetite–pyrite; (ii) the syn-ore stage is composed of galena, sphalerite, tetrahedrite and stefanite; and (iii) the post-ore stage is composed of carbonates, pyrite, arsenopyrite and minor galena. The vein type mineralization is hosted by Jurassic amphibolites and veins terminate within overlying serpentinites. Mineralized listwaenites are developed along the serpentinite–amphibolite interface. The reserves are estimated to 1.7 Mt of ore containing in average 7.6% lead, 2.9% zinc, and 102 g/t silver. Sulfides from the pre- and syn-mineralization assemblage of the vein- and listwaenite-types of mineralization from the Crnac Pb–Zn–Ag deposit have been analyzed using microprobe, crush-leachates and sulfur isotopes.The pre-ore assemblage precipitated under high sulfur fugacities (f(S2) = 10− 8–10− 6 bar) from temperatures ranging between 350 °C and 380 °C. Most likely water–rock reactions, boiling and/or increase of pH caused an increase of δ34S of pyrite toward upper levels within the deposit. The decomposition of pre-ore pyrrhotite to a pyrite-magnetite mixture occurred at a fugacity of sulfur from f(S2) = 8.7 × 10− 10 to 9.6 × 10− 9 bar and fugacity of oxygen from f(O2) = 2.4 × 10− 30 to 3.1 × 10− 28 bars, indicating a contribution of an oxidizing fluid, i.e. meteoric water during pre-ore stages of hydrothermal activity. The crystallization temperatures obtained by the sphalerite-galena isotope geothermometer range from 230 to 310 °C. The δ34S values of pre- and syn-ore sulfides (pyrite, galena, sphalerite, δ34S = 0.3–5.9‰) point to magmatic sulfur. Values of δ34S of galena and sphalerite are decreasing upwards due to precipitation of early formed sulfide minerals. Post-ore assemblage precipitated at temperature below 190 °C.Based on data presented above, we assume two fluid sources: (i) a magmatic source, supported by sulfur isotopic compositions within pre- and syn-ore minerals and a high mol% of fluorine found within pre- and syn-ore leachates, and (ii) a meteoric source, deduced by coincident pyrite–magnetite intergrowth, sulfur isotopic trends within syn-ore minerals and decrease of crystallization temperatures from the pre-ore stage (380–350 °C), towards the syn-ore (310–215 °C) and post-ore stages (< 190 °C). Post-ore fluids are Na–Ca–Mg–K–Li chlorine rich and were modified via water–rock reactions. Simple mineral assemblage and sphalerite composition range from 1.5 to 10.1 mol% of FeS catalog Crnac to a group of intermediate sulfidation epithermal deposit.► Intermediate sulfidation, epithermal Pb-Zn-Ag vein and listwaenite type of deposit Crnac, Western Vardar zone. ► Pre-ore pyrite, arsenopyrite, pyrrhotite, quartz, kaolinite; syn-ore galena, sphalerite, tetrahedrite; post-ore carbonates. ► Pre-ore stage: f(S2) = 10− 8–10− 6 bar to f(S2) = 8.7 × 10− 10 to 9.6 × 10− 9 bar; f(O2) = 2.4 × 10− 30 to 3.1 × 10− 28 bars, t = 350–380 °C. ► Syn-ore stage: t = 230–310 °C; d34S = 0.3 – 5.9 ‰. ► Post-ore stage: t < 190 °C; Na-Ca-Mg-K-Li chlorine rich fluid. ► Mixture of magmatic and meteoric water.

The specularite deposit at Waldenstein is an epigenetic replacement/vein-type hematite mineraliza... more The specularite deposit at Waldenstein is an epigenetic replacement/vein-type hematite mineralization with distinct alteration zones. It is situated in highly metamorphosed schists and gneisses of the Koralm Crystalline Complex. Sericitization and chloritization are strictly bound to this alteration and occur within a few meters of the hematite veins. Radiometric dating of the sericitization and the implicity of the mineralization yield a Middle Eocene age. Petrographic evidence proves an early, relatively reduced paragenesis (magnetite, ilmenite) being partly replaced by hematite and chlorite during the main phase of ore formation. Fluid inclusion and stable isotope investigations indicate that formation temperatures were approximately 300°C during the main stage and decreased to 200°C in the latest stage of the hydrothermal event. The H-isotope compositions of chlorites and of fluid inclusions in quartz indicate the influence of seawater. This also explains the high salinities determined by fluid inclusion studies (20-30% NaC1 equiv.). According to the genetic model presented in this paper the hydrothermal activity started when the deformation accompanying the uplift of the Koralm Crystalline Complex passed from a ductile to brittle regime (Middle Eocene). The brittle faults acted as channelways for rising, deep fluids, probably of metamorphic origin. Temperature differences between the different uplifting crustal segments supw. Prochaska ported fluid circulation. Precipitation of the ore occurred at shallow crustal levels where the hydraulic regime was dominated by seawater, and oxidation of the original reducing fluids took place.

International Journal of Earth Sciences, 2011

Basal hydraulic breccias of alpine thin-skinned Muráň nappe were investigated by means of cathodo... more 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.

The study aims to investigate the role of hydrothermal fluids in the formation of talc and magnes... more The study aims to investigate the role of hydrothermal fluids in the formation of talc and magnesite deposits. These deposits occur in manifold geological and tectonical settings such as stockworks and veins within ultramafite hostrocks and monomineralic lenses within marine platform sediments. Along shear zones talc mineralizations may occur as a result of tectonical and hydrothermal activity. To understand the role of the fluids for the genesis of the mineralization, deposits in different geological and tectonical settings are investigated: Talc mineralization within in magnesite in low-grade palaeozoic nappe complexes (Gemerska Poloma, Slovakia): The magnesite body lies within the Gemer unit of the Inner Carpathians consisting of Middle Triassic metacarbonates and Upper Triassic pelagic limestones and radiolarites. The talc mineralization is bound to crosscutting veins. Two metamorphic events can be distinguished, one during Variscan orogeny and one related to the Alpine orogeny leading to the formation of talc along faults in an Mg carbonate body (Radvanec et al, 2004).The origin of the fluids as well as the tectonic events leading to the mineralization is still widely unknown. Talc mineralization in shearzones within Palaeozoic meta sedimentary rocks (Sa Matta, Sardinia): Variscan granitoids intruded Palaeozoic meta sedimentary rocks and were overprinted be NE striking tectonic structures that host talc mineralizations. The origin of Mg and fluids leading to the mineralization is still not answered satisfactorily (Grillo and Prochaska, 2007) and thus a tectonic model for the genesis of the talc deposit is missing. Talc mineralization within UHP pre-Alpine continental crust (Val Chisone, Italy): The talc deposit forms part of the Dora-Maira Massif. Geologicaly the massif derived from a Variscan basement that includes post-Variscan intrusions. The talc mineralization occurs as a sheetlike, conformable body. A possible tectonic emplacement of talc along shear surfaces was proposed by Sandrone & Zucchetti, 1988. Magnesite and talc bearing shearzones in ultramafic hostrocks (Lahnaslampi & Horsmanaho, Finland): Both deposits are situated in the Proterozoic schist belt where the talc-magnesite rocks at Lahnaslampi are associated with minor serpentine breccias. The steatitization took place in two different stages: During prograde metamorphism with H2O-dominated solutions and at declining temperature and pressure in the presence of CO2-bearing fluids that resulted in the main steatitization along tectonic structures. A combined geological, petrological and geochronological is chosen to resolve mechanism of mineralisation within the different tectonic setting. Different phases of mineral formation are first distinguished by pertrological and structural field work and then dated by radiometric techniques. Fluid species and chemical environment during mineralisation is resolved by geochemical techniques and stable isotope studies. References Grillo, S., Prochaska, W. (2007): Fluid Chemistry and Stable Isotope Evidence of Shearzone related Talc and Chlorite Mineralizations in Central Sardinia-Italy, In: Conference Abstracts SGA-Meeting. Radvanec, M., Koděra, P., Prochaska, W. (2004): Mg replacement of the Gemerska Poloma talk-magnesite deposit, Western Carpathians, Slovakia. Acta Petrologica Sinica, 20, 773-790. Sandrone, Zucchetti (1988): Geology of the Italian high-quality cosmetic talc from the Pinerolo district (Western Alps). Zuffar' Days - Symposium held in Cagliari, 10-15

Mineralium …, 2009

The Zálesí vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the nor... more The Zálesí vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the northern margin of the Bohemian Massif. The mineralization is composed of three main stages: uraninite, arsenide, and sulfide. The mineral assemblages formed at low temperatures (~80 to 130°C, locally even lower) and low pressures (<100 bars). The salinity of the aqueous hydrothermal fluids (0 to 27 wt.% salts) and their chemical composition vary significantly. Early fluids of the oldest uraninite stage contain a small admixture of a clathrate-forming gas, possibly CO2. Salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines [δ 18O around +2‰ relative to standard mean ocean water (SMOW)] with meteoric waters (δ 18O around −4‰ SMOW). The fluid is characterized by highly variable halogen ratios (molar Br/Cl = 0.8 × 10−3 to 5.3 × 10−3; molar I/Cl = 5.7 × 10−6 to 891 × 10−6) indicating a dominantly external origin for the brines, i.e., from evaporated seawater, which mixed with iodine-enriched halite dissolution brine. The cationic composition of these fluids indicates extensive interaction of the initial brines with their country rocks, likely associated with leaching of sulfur, carbon, and metals. The brines possibly originated from Permian–Triassic evaporites in the neighboring Polish Basin, infiltrated into the basement during post-Variscan extension and were finally expelled along faults giving rise to the vein-type mineralization. Cenozoic reactivation by low-salinity, low-δ 18O (around −10‰ SMOW) fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite-like mineral aggregates.

Mineralogy and Petrology, 2009

The Petrova and Trgovska Gora Mts. (Gora=Mountain) are Variscan basement units incorporated into ... more The Petrova and Trgovska Gora Mts. (Gora=Mountain) are Variscan basement units incorporated into the northwestern Dinarides during the Alpine orogeny. They host numerous siderite-quartz-polysulphide, siderite-chalcopyrite, siderite-galena and barite veins, as well as stratabound hydrothermal-replacement ankerite bodies within carbonates in non-metamorphosed, flysch-like Permo-Carboniferous sequences. The deposits have been mined for Cu, Pb, Ag and Fe ores since Medieval times. Fluid inclusion studies of quartz from siderite-polysulphide-quartz and barite veins of both regions have shown the presence of primary aqueous NaCl−CaCl2±MgCl2−H2O±CO2 inclusions. The quartz-sulphide stage of both regions show variable salinities; 2.7–26.2 wt% NaCl eq. for the Trgovska Gora region and 3.4–23.4 wt% NaCl eq. for the Petrova gora region, and similar homogenisation temperatures (100–230°C). Finally, barite is precipitated from low salinity-low temperature solutions (3.7–15.8 wt % NaCl equ. and 115–145°C). P-t conditions estimated via isochore construction yield formation temperatures between 180–250°C for the quartz-sulphide stage and 160–180°C for the barite stage, using a maximum lithostatic pressure of 1 kbar (cc. 3 km of overburden). The sulphur isotope composition of barite from both deposits indicates the involvement of Permian seawater in ore fluids. This is supported by the elevated bromium content of the fluid inclusion leachates (120–660 ppm in quartz, 420–960 ppm in barite) with respect to the seawater, indicating evaporated seawater as the major portion of the ore-forming fluids. Variable sulphur isotope compositions of galena, pyrite and chalcopyrite, between −3.2 and +2.7‰, are interpreted as a product of incomplete thermal reduction of the Permian marine sulphate mixed with organically- and pyrite-bound sulphur from the host sedimentary rocks. Ore-forming fluids are interpreted as deep-circulating fluids derived primarily from evaporated Permian seawater and later modified by interaction with the Variscan basement rocks. 40Ar/39Ar data of the detrital mica from the host rocks yielded the Variscan age overprinted by an Early Permian tectonothermal event dated at 266–274 Ma. These ages are interpreted as those reflecting hydrothermal activity correlated with an incipient intracontinental rifting in the Tethyan domain. Nevertheless, 75 Ma recorded at a fine-grained sericite sample from the alteration zone is interpreted as a result of later resetting of white mica during Campanian opening/closure of the Sava back arc in the neighbouring Sava suture zone (Ustaszewski et al. 2008).

… Institute of the Hungarian Academy of …, 2001

Economic Geology, 1995

... carbonate-dominated rocks. Most deposits (eg, Tux-Lanersbach, Klamm Aim) are situated at the ... more ... carbonate-dominated rocks. Most deposits (eg, Tux-Lanersbach, Klamm Aim) are situated at the southern margin of the lower Austroalpine Innsbruck quartz phyllite zone, close to the tectonically underlying Penninit units. About 60 ...