Lagerstättengenetische Untersuchungen im Bereich der Uranerz-Struktur Wäldel/Mähring (NE-Bayern)

Zusammenfassung Das Uranvorkommen bei Mähring/Oberpfalz liegt im Grenzbereich Moldanubikum-Saxothuringikum. Die erzführenden Strukturen streichen ± N–S (Gang II) und NNWSSE (Gang I). Sie durchschlagen ein aus Kalifeldspat-Biotit-Granitoiden und chloritisierten Biotitglimmerschiefern aufgebautes Nebengestein vermutlich präkambrischen Alters. Die Gangquarze liegen in mehreren Generationen vor; sie werden stark kataklastisch beansprucht und umgelagert. In den Drusen und im Intergranularraum des Quarzganges schieden sich die Phosphate, Eisenbisulfide, Molybdänsulfide und U-Titanate, U-Oxide und U-Silikate ab. Diese Vererzung läßt sich mit der in Höhensteinweg bei Poppenreuth aufgefundenen monotonen S-akkordanten U-Mineralisation vergleichen. Sie weist innerhalb der Vererzung eine nebengesteinsbezogene Bindung der Uranerzminerale dahingehend auf, daß die Urantitanate an die chloritisierten Nebengesteinsbereiche gebunden sind, während die Uranoxide vornehmlich in den reinen Gangquarzen konzentriert sind. Eine polymetallische U-Mineralisation kommt nicht vor. Vergleiche mit Uranerzvorkommen in der CSSR legen niedrig-thermale Bildungsbedingungen für das Vorkommen Wäldel nahe. Die Elementassoziation U-P-Mo-C deutet auf eine Karbonatoder/und Schwarzschiefereinschaltung in der Bunten Gruppe als Muttergestein hin. Die Elementanreicherung geht primär auf eine Mobilisationen durch den jungvariszischen Magmatismus zurück. Eine postvariszische Umlagerung ist nach den Spurenelemenlvergleichen mit anderen U-Vorkommen und nach den mineralogischen Daten (z. B. kein radiogener Bleiglanz, viel metamorphes Bitumen) anzunehmen. Die Lagerstätte wird nicht als Gangvorkommen s. Str., sondern als mineralisierte Strukturzone bezeichnet. Diese Strukturzonen weisen häufig eine sehr große Teufenerstreckung auf.

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The uranium occurrence near Mähring/Upper Palatinate is situated in the border zone between the Moldanubian and Saxothuringian. The ore-bearing structures run NNW-SSE (lode I) and more or less N-S (lode II). They intersect Precambrian country rocks composed of potassium feldspar-biotite-granitic-mobilisates and chloritised biotite mica schists. The gangue material has formed at different stages and has been affected by intensive cataclastie deformation and recrystallisation. The phosphates, iron sulfides, molybdenum sulfides and U-titanates, U-oxides and U-silicates crystallised in cavities and interstices of the vein quartz. The whole mineralisation can well be compared with the monotonous subconcordant U-mineralisation found in the Höhensteinweg uranium deposit, which is in the neighbourhood of the Wäldel uranium deposit. There is a close relationship between the type of U-mineral and the lithology of the wall rock. Brannerites, for example, are closely associated with chloritised rocks, whereas U-oxides are predominantly encountered in pure vein quartz. No polymetallic U-mineralisation has been found up to now. Comparisons with U-occurrences in Czechoslovakia point to a low temperature of formation for this U-mineralisation. Judgeing from the main elements such as U, P, Mo and C, the mineralisation may have been derived from a deeper-lying metachert and/or carbonate horizon of the Varied Group. The late Variscan thermal events were probably responsible for the mobilisation of these elements. Mineralogical features (e.g. no radiogenic galena, impsonites) and trace element distribution suggest that this mineralisation was redeposited during the Alpidic period. The deposit cannot be classified as a vein-type deposit s.s. as has been done in the past, since it lacks any gangue material paragenetically associated with the U-ores. It is better described as a mineralised fault zone. They are well known for their deep reaching ore bodies.

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Résumé Le gisement d'uranium de Mähring, en Haut-Palatinat, se trouve sur la limite des zones moldanubienne et saxo-thuringienne. Les structures minéralisées sont orientées ± N-S (filon II) et NNW-SSE (filon I). Elles recoupent une roche encaissante d'âge probablement précambrien, constituée de granitoides à biotite et feldspath potassique et de micaschistes chloritisés à biotite. Plusieurs générations se retrouvent dans le quartz filonien qui a subi une forte contrainte cataclastique et a été remanié. Des phosphates, des disulfures de fer, des sulfures de molybdène, des titanates, des oxydes et des silicates d'uranium se sont déposés dans les géodes et dans les espaces intergranulaires du filon de quartz. On peut comparer ce gite avec le minéralisation uranifère, monotone, de plan S, de Höhensteinweg, près de Poppenreuth. Le fait que les titanates uranifères sont liés aux zones chloritisées de la roche encaissante, alors que les oxydes d'uranium sont le plus souvent limités aux filons de quartz pur, indique une liaison avec lá roche encaissante au sein de la minéralisation. Il n'y a pas de minéralisation polymétallique uranifère. La comparaison avec d'autres gisements d'uranium d'Europe centrale suggère une formation à basse température pour le gisement dé Wäldel. L'association des éléments U-P-Mo-C indique une intercalation de schistes noirs et/ou de carbonates dans la roche-mère, la «Bunte Gruppe». A l'origine, l'enrichissement des éléments est dû à une mobilisation contrôlée par des phénomènes magmatiques d'une phase jeune du cycle varisque. La comparaison des éléments en traces avec ceux d'autres gisements d'uranium, ainsi que les données minéralogiques (pas de galène radiogène, beaucoup de bitume) suggèrent qu'il y a eu un remaniement et une phase de minéralisation postvarisques. Ce gisement n'est pas considéré comme un gisement filonien au sens strict, mais plutôt comme une «zone structurale minéralisée». Ce genre de zones structurales montre souvent une très grande étendue en profondeur.

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( ) Moldanubikum — Saxothuringikum. N—S ( 11). NNW—SSE ( 1). , - , , - . , , . ; , , , , . Hohensteinweg Poppenreuth. , , , , — . . , Wäldel. U, , . . (.: , ) . , . .

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Der Begriff Struktur wird zur Kennzeichnung eines im Streichen verfolgbaren Erzvorkommens verwendet. Es handelt sich um einen rein deskriptiven Begriff, der auf den durch die Exploration gewonnenen Daten basiert und frei von einer präjudizierenden lagerstättengenetischen Deutung sein soll.     

H2O diffusion in dacitic and andesitic melts

The diffusion of water in dacitic and andesitic melts was investigated at temperatures of 1458 to 1858 K and pressures between 0.5 and 1.5 GPa using the diffusion couple technique. Pairs of nominally dry glasses and hydrous glasses containing between 1.5 and 6.3 wt.% dissolved H₂O were heated for 60 to 480 s in a piston cylinder apparatus. Concentration profiles of hydrous species (OH groups and H₂O molecules) and total water (C_H2Ot = sum of OH and H₂O) were measured along the cylindrical axis of the diffusion sample using IR microspectroscopy. Electron microprobe traverses show no significant change in relative proportions of anhydrous components along H₂O profiles, indicating that our data can be treated as effective binary interdiffusion between H₂O and the rest of the silicate melt. Bulk water diffusivity (D_H2Ot) was derived from profiles of total water using a modified Boltzmann-Matano method as well as using fittings assuming a functional relationship between D_H2Ot and C_H2Ot. In dacitic melts D_H2Ot is proportional to C_H2Ot up to 6 wt.%. In andesitic melts the dependence of D_H2Ot on C_H2Ot is less pronounced. A pressure effect on water diffusivity could not be resolved for either dacitic or andesitic melt in the range 0.5 to 1.5 GPa. Combining our results with previous studies on water diffusion in rhyolite and basalt show that for a given water content D_H2Ot increases monotonically with increasing melt depolymerization at temperatures >1500 K. Assuming an Arrhenian behavior in the whole compositional range, the following formulation was derived to estimate D_H2Ot (m²/s) at 1 wt.% H₂O_t in melts with rhyolitic to andesitic composition as a function of T (K), P (MPa) and S (wt.% SiO₂):

     

Synsedimentary faults and amalgamated unconformities: Insights from 3D-seismic and core analysis of the Lower Triassic Middle Buntsandstein, Ems Trough, north-western Germany

The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by the tectonic pulses associated with the earliest phases of Tethyan and Arctic–North Atlantic rifting. Effects of the differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. Such unconformities are most obvious in areas occupied by fault-controlled intra-basinal highs (swells). In that areas, stratigraphic loss may comprise entire Lower and Middle Buntsandstein formations and in places remnant Middle Buntsandstein successions directly rest on Permian strata. Analysis of 3D-seismic data and well logs combined with high-resolution sedimentological logging of drillcores at the western margin of the Ems Trough (NW Germany) reveals details of synsedimentary tectonic control on sequence development. Early Triassic extensional faulting of basement blocks provided stepwise addition of accommodation space for continental sequences by growth faulting along north–south oriented fault zones blocks on the flanks of the East Netherlands High. This process is most evident during the development of the Hardegsen Unconformity, which is characterised by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs.     

Numerical study of the performance of tunnel plugs

High axial flow rates within and along tunnels, excavated for deposition of high level nuclear waste, may increase the transport capacity of potential escape routes for radionuclides that have been released to the buffer surrounding the waste canisters, or to the tunnel backfill materials, from leaking fuel canisters. High flow rates may be found if the tunnel interior has a high permeability, either initially due to the composition of the backfill material or at later times due to degradation of low permeability backfill material components. If a disturbed rock zone, a DRZ, of increased permeability was created as a result of direct damage done to the wall region during tunnel excavation, this zone may contain additional possible escape routes. Low-permeability tunnel plugs, keyed into slots cut in the rock walls, have been suggested as means of reducing axial flow rates. This paper deals with different aspects of such tunnel-plug systems. A preliminary estimate of the potential for tunnel plugs to reduce axial flow rates is made using analytical expressions. A number of numerical techniques are employed to investigate the hydraulic, mechanical and hydromechanical performance. These include μFLOW (FEM flow calculations), FLAC (finite difference mechanical calculations) and 3DEC (distinct element mechanical calculations). The mechanical calculations concern the mechanical stability in the rock surrounding the slot and permeability changes in that rock caused by stress redistribution. The results show that the effects of tunnel plugs are very significant in most cases. A discussion on the validity of the results and the applicability of the used methods is provided.     

High-Latitude Springtime Photochemistry. Part Ii: Sensitivity Studies of Ozone Production

A seven-year record of surface ozone measurements from Denali NationalPark, Alaska shows a persistent spring maximum. These data, combined withmeasurements of NO_x, hydrocarbons, O₃, and PANfrom a continental site in Alaska during the spring of 1995 are used as thebasis for a sensitivity study to explore tropospheric photochemistry in thisregion. Because of the relatively high concentrations of NO_x(mean of 116, median of 91 pptv), the net tendency was for photochemicalozone production. The range of net O₃ production for averageconditions measured at this site during spring is between 0.96–3.9ppbv/day depending on the assumptions used; in any case, this productionmust contribute to the observed springtime maximum in O₃.Model calculations showed that of the anthropogenic ozone precursors, onlyNO_x had a strong effect on the rate of ozone production; themeasured concentrations of anthropogenic hydrocarbons did not significantlyaffect the ozone budget. Naturally produced biogenic hydrocarbons, such asisoprene, may also have a significant effect on ozone production, even atconcentrations of a few 10's of pptv. An observed temperature-isoprenerelationship from a boreal site in Canada indicates that isoprene may bepresent during the Alaskan spring. Measurements of isoprene taken duringthe spring of 1996 suggest that reactive biogenic hydrocarbon emissionsbegin before the emergence of leaves on deciduous trees and that theconcentrations were sufficient to accelerate ozone production.     

Study of metal aerosol systems as a sink for atmospheric SO2

The chemical removal of SO₂ in the presence of different aerosol systems has been investigated in laboratory experiments using a dynamic flow reactor. The aerosols consisted of wetted particles containing one of the following substances: MnCl₂, Mn(NO₃)₂, MnSO₄, CuCl₂, Cu(NO₃)₂, CuSO₄, FeCl₃, NaCl. The SO₂ removal rate R was measured as a function of the SO₂ gas phase concentration (SO₂)_g, the spatial metal concentration C_Me, and the relative humidity rH in the reactor. A first-order dependence with regard to (SO₂)_g was observed for each type of aerosol. For the Mn(II) and Cu(II) aerosols R was found to be a non-linear function of C_Me except for MnSO₄ and Cu(NO₃)₂ particles. The removal rate showed a significant increase with the relative humidity particularly when rH was close to the deliquescence point of the wetted particles. Among the Mn(II) and Cu(II) aerosols investigated Mn(NO₃)₂ was found to be most efficient for the chemical removal of SO₂ at atmospheric background conditions, especially in haze and fog droplets. The results further indicate that the catalytic oxidation of S(IV) in such aerosol systems may be as efficient as its oxidation by H₂O₂ in cloud water.     

Antimoniferous mineralization from the Mid-European Saxothuringian Zone: mineralogy,geology, geochemistry and ensialic origin

In the North Bavarian Basement (FR Germany) as well as in the Thuringian Forest (GDR) both of which belonging to the Saxothuringian Zone antimony mineralizations have been worked up to the early fifties. Mineralogical and geological investigations led to the following classification of antimony ore deposits and -concentrations:

1. Stratabound and stratiform fahlore (Fahlerz) mineralization in Silurian and Lower Devonian black shales.
2. Sulphosalt- and stibnite-bearing veins (partly associated with native gold) in wall rocks of the Late Variscan granites.
3. Monometallic and monomineralic antimony lodes along anticlinal structures.
4. Sulphosalt-bearing lead-zinc veins.

Antimony in the black shales was concentrated during late diagenetic cementation along with copper. The sulpho-salt-bearing stibnite veins in the metamorphic country rocks of the granites are genetically associated with the granitic intrusions nearby. This is proved by trace element chemistry and structural as well as mineralogical features of those veins. U/Pb age dating of contemporaneous pitchblende from the »polymetallic uranium paragenesis« from Hoehensteinweg uranium deposit yielded a late Variscan age of formation for these veins of type 2. Early Paleozoic rocks (metavolcanics) are suggested to have been the parent material for these granite-related Sb concentrations. However the monotonous Sb veins are more akin to the basic protore in deeper crustal sections. The thermal aureole of a deep-seated heat source is preserved by the Ag/Sb ratio of galena in Pb-Zn veins (type 4), which shows a marked variation along the SW plunging Berga Anticline from increased Ag/Sb ratios near the core of the anticline towards reduced values in mining sites more peripheral to this fold structure. Pb isotopes of stibnite as well as Pb sulphides point to a crustal derivation of both elements. An in-situ re-deposition and leaching of Sb from the wall rocks as well as antimoniferous black shales may be ruled out. It has to be emphasized that intra-crustal mass movements (A subduction) and the late Vanscan igneous activity are the major factors controling release of Sb from the Early Paleozoic low metal concentrations within metavolcanic rocks and subsequent discharge of Sb-bearing fluids within joints and fractures related to late Variscan tectonic movements. A schematic exploration concept is outlined.     

Interferierende Kleinfaltensysteme und ihre Bedeutung für den Bau des Tuxer-Joch-Gebietes (Tauernfenster,Tirol)

Zusammenfassung Der komplizierte Decken- und Faltenbau im inneren Tuxertal wurde mit einer hier bislang nicht angewandten Arbeitsmethode zur Analyse interferierender Kleinfaltensysteme untersucht. Dabei wurden gebogene Kleinfaltenachsen imSchmidt'schen Netz nicht — wie sonst praktiziert — durch Punkte, sondern durch Kurven im SinneRamsays dargestellt. Aufgrund detaillierter Geländebeobachtungen und der Auswertung entsprechender Kurvendiagramme konnte eine relativstratigraphische Einstufung und konstruktive Rückformung von Falten in mehrphasig beanspruchten Gesteinen vorgenommen werden. Bisherige Korrelationen zwischen Achsenrichtungen und Achsenaltern müssen aufgegeben werden, weil während ein und derselben Deformationsphase geprägte Achsen aufgrund späterer Deformation beliebige Streichrichtungen aufweisen bzw. verschieden alte Achsen gleich orientiert sein können. — Die angewandte Arbeitsweise führte u. a. zur Entdeckung einer f₂-Schlingentektonik im Tuxertal und ermöglichte eine besser als bisher begründete Abgrenzung zwischen Wolfendorndecke und Glocknerdecke im Tuxer-Joch-Gebiet.

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The complicated nappe and fold structures in the inner Tuxer valley were examined with a new method, analyzing systems of interfering small-scale folds, which up to now has not been used in this area. Connected with this method curved fold axes in theSchmidt net were not depicted by points, as usual, but by curves in the meaning ofRamsay. Based upon detailed field observations and the evaluation of curve diagrams a relative stratigraphic classification and constructive rebound of folds in multiphase deformed rocks could be taken up. Previous correlations between directions and ages of axes must be abandoned, because axes formed during one and the same phase of deformation may show any striking because of later deformation, or axes of different ages may show the same orientation respectively. — The working method used, led to the discovery of a f₂-vortex-tectonics in the Tuxer valley, thus making possible a delimitation between the Wolfendorn nappe and the Glockner nappe in the Tuxer Joch area that proved to be better founded than former attempts.

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Résumé Le style compliqué des nappes et des plis dans la vallée inférieure de Tux (Tuxertal) a été analysé par une méthode de travail non appliquée jusqu'ici pour l'analyse de système de petits plis interférants. On a resprésenté des axes de petits plis incurvés sur un canevas de Schmidt par des courbes au sens de Ramsay, et non par des points comme cese fait d'habitude. A partir d'observations détaillées de terrain et de résultats issus des diagrammes de courbe il a été permis d'aborder l'intégration stratigraphique relative et une reconstitution des plis dans les roches ayant subi plusieurs phases de déformation. Les corrélations acceptées jusqu'aujourd'hui concernant la direction et l'âge des axes doivent être abandonnées pour deux raisons; les axes issus de la même phase de déformation peuvent montrer des sens de direction quelconques à la suite des déformations suivantes, ou bien des axes d'âge différents peuvent prendre la même orientation. La méthode de travail appliquée ici a permis la découverte d'un «Schlingentektonik» dans la vallée de Tux et a favorisé ainsi une meilleure limitation entre la nappe de Wolfendorn et la nappe du Glockner dans la région du Tuxerjoch.

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