Jörg Hammer

Fault-related barriers for uranium transport

This contribution presents data on the long-term retentive ability of diverse mineral infill of hydraulically active faults in respect to radionuclides migrating within the vadose zone of crystalline massifs by the example of the vein-type Tulukuevskoe uranium deposit in SE Transbaikalia, Russia.

Experimental deformation of coarse-grained rock salt to high strain

The processes and deformation mechanisms (e.g., dislocation creep, pressure solution, grain boundary sliding, and recrystallization) of rock salt are still a matter of debate. In order to fill this gap, high strain constriction experiments at 345°C, atmospheric pressure and a strain rate of ~10−7 s−1 have been conducted on natural halite cuboids (60 × 60 × 45 mm) from the Morsleben mine of Northern Germany. Most samples were almost single crystals and contain a small amount of smaller grains (10–26%). The grain boundaries are decorated with fluid inclusions. The experiments were stopped at different final strains (ey = z of ~10, 20, 30, and 40%) corresponding to a maximum strain (ex) range of 20–170%. The halite is deformed by dislocation creep, and the size of developed subgrains corresponds to the applied stress. The combined Schmid factor and subgrain boundary analysis indicate that slip was largely accommodated by the {110}   slip systems, with possible minor contribution by slip on the {100}   slip systems. Some of the deformed samples show evidence of grain boundary migration. In addition, subgrains with small misorientations form that result in large cumulative misorientations within a single grain (>40°). However, no subgrain rotation recrystallization is observed (i.e., misorientation angles are <10°). All the experiments show strain hardening, suggesting that recrystallization by grain boundary migration was not extensive and did not reset the microstructure. The experiments show that high finite strain in coarse-grained relatively dry rock salt can be accommodated by dislocation creep, without extensive dynamic recrystallization.

Uranium Mineralization in Fractured Welded Tuffs of the Krasnokamensk Area: Transfer from Ancient to Modern Oxidizing Conditions

The main aim of this contribution is to describe the primary controls of the hydrothermal mineralization, the preferential pathways for ancient and recent meteoric water infiltration, mineral-chemical modification of the wall rocks, and transformation of uranium mineralization in the context of redox front propagation through unsaturated fractured porous welded tuffs. The data on the veintype Tulukuevskoe uranium deposit in SE Transbaikalia, Russia are applied for modeling of uranium migration and deposition of secondary concentrations using quasi-stationary state approximation (QSSA) approach.

Uranium and Molybdenum transfer within the oxidized zone of uranium deposit

Total Dissolved Solids (ion composition), concentrations of some trace elements and pH-values determination results of vein-fractured water samples from the open pit of the Tulukuevskoe U-Mo deposit in acid volcanic rocks of Transbaikalia are presented. Rest upon obtained data it is possible to assume that in the southern part of the open pit a flat-lying ore-bearing untapped structure exists. An inverse relationship between the content of hydrocarbonate ions in veinfractured waters and concentration of uranium is presented.

Stress-time context of fault permeability at the Krasnokamensk Area SE Transbaikalia

The main aim of the contribution is to combine data on the consecutive stages of deformation, inflow and migration of palaeofluids and accumulation of mineral filling with uranium traces within the faulted-fractured environment at the Krasnokamensk Area, SE Transbaikalia, Russia. Object of examination is a framework of fault zones transecting the Proterozoic-Paleozoic granitic unit to the extent of northwestern part of uranium-bearing Streltsovskaya caldera of Mesozoic age. Considerations of stress- and permeability-time relationships in faulted-fractured zones were taken with account of stress and strain dependencies within fluid saturated rock massifs at crustal seismogenic level. Stress-time consecution of fault zone permeability was developed using set of fieldwork and lab tests including structural-geological survey, fault slip data analysis, mineral-chemical diagnostics, microstructural observations, and radiographic studies. Practical applications of obtained data for solving uranium mining and environmental issues are indicated in conclusion.

Uranium transfer around volcanic-associated uranium deposit

Only about 60% of the annual consumption in the nuclear fuel cycle is provided by primary uranium production at present. Hence, a strong demand for additional exploration of additional uranium resources is identified in many countries. Hence, a large potential exists for unconventional uranium deposits such as mobilization areas in the surroundings of known deposits. Besides environmental aspects a deep understanding concerning the migration and accumulation behaviour of uranium isotopes and related elements is necessary. As an example we will present data of the Tulukuevskoe deposit, SE Transbaikalia, Russia. Here, primary UO2 mineralization is mined from the Tulukuevsky open pit (TOP). The pitchblende is subject of secondary remobilization and transformations within the vadose zone of the deposit. Seven years of field and laboratory studies indicated that a uranium speciation dominated by carbonate complexes and gradually shifted from the UO2(CO3)3 4- to the UO2(CO3)2 2-species field with enhanced formation of uranylcarbonates (Petrov 2005). Three remobilization areas varying in their mineral-chemical composition, transport parameters and the oxidizing degree of the welded tuffs are conceptualized. Sensitivity to the sequential variations in hydrochemistry and isotopic composition of fractured and meteoric waters is considered in the context of spatial-temporal development of the redox front. Identification and exploration of the redox front and of primary and secondary uranium enrichments is facilitated by the upmu-energy dispersive x-ray fluorescence (EDXRF) technique that allows the high resolution in-situ determination of a number of elements simultaneously at the microscopic scale of typically 100 upmum (Rammlmair et al. 2006). This method is fast and useful in order to localise primary uranium minerals as well as mobilised and secondary uranium-bearing phases. The results of the study are interesting also as an analogue of destruction of deep repository of nuclear waste.