ALBERT

Notizen: Abstract Precambrian granulites of the Aldan shield in southern Yakutia, USSR, form a massif of 200,000 km2 bounded by younger fold-belts to the south, west and east. The massif consists of several blocks that reflect a primary heterogeneity of composition and differences in structural and thermodynamic evolution of different parts of the area. According to structural and petrological data the massif can be divided into two megablocks: eastern Aldan and western Aldan. They are separated by a narrow meridional fold-belt. Structural evolution of this central zone was determined by the geodynamics of the mega-blocks and was completed in the late Archaean. Towards the south, this central zone is ‘transformed’into the relatively small Sutam block adjoining the Stanovoy fold-belt that bounds the Aldan shield on the south. The Sutam block is separated from the other structural units of the Aldan shield by a system of north trending grabens filled by post-Archaean sediments.The Aldan shield is composed of Archaean high-grade granulites, while the Stanovoy fold-belt, to the south, consists of highly foliated Proterozoic rocks metamorphosed under relatively lower-grade conditions. However, relics of the granulites are mapped within the fold-belt. They contain high-grade assemblages (e.g. Opx + Sil + Qz, Sap + Qz, Opx + Gr + Sil, etc.). One of the relics, the Tokskii block, which is only slightly touched by diaphthoresis, is located in the southeastern part of the Stanovoy fold-belt. Metamorphic conditions of the Tokskii block are compared with those of the Sutam block and a similar evolution of the units is revealed.Mineral assemblages and mineral compositions do not vary within each unit, but they change in a north-south direction. The Opx + Sil + Qz assemblage has been found only in Sutam and Tok, but not in eastern Aldan and western Aldan. The Sap + Qz assemblage has been found in the Tokskii block but has not yet been found in the Sutam block. The pyrope content in garnets, from metapelites of both blocks, is significantly higher than that from the Aldan (eastern and western blocks) rocks to the north. The most important assemblages from different units of the Aldan shield have been studied using the electron microprobe in order to unravel the metamorphic evolution of the granulites and thus to deduce the thermodynamic regime of this evolution. A geodynamic model for the Aldan shield is discussed in terms of Archaean island arc development.

Notizen: The 3–D model of the Earth, as obtained with a brand new investigative technique, is discussed. However an international collaborative project, involving researchers from the whole world, has uncovered a severe systematic error in the new data acquisition system making the results of this new model highly questionable.

Notizen: Interlayer slipping breccia-type gold deposit – a new type of gold deposit, defined recently in the northern margin of the Jiaolai Basin, Shandong Province, China – occurs in interlayer slip faults distributed along the basin margin. It has the features of large orebody thickness (ranging from 14 m to 46 m, with an average thickness of 30 m), shallow embedding (0–50 m thickness of cover), low tenor of gold ore (ranging from 3 g/t to 5 g/t), easy mining and ore dressing. This type of gold deposit has promising metallogenic forecasting and potential for economic exploitation.A ground gamma-ray survey in the Pengjiakuang gold-ore district indicates that the potassium/thorium ratio is closely related to the mineralization intensity, i.e. the larger the potassium/thorium ratio, the higher the mineralization. The gold mineralized alteration zone was defined by a potassium/thorium ratio of 0.35. A seismic survey confirms the location of the top and bottom boundaries and images various features within the Pengjiakuang gold mineralization belt. The gold-bearing shovel slipped belt dips to the south at an angle of 50–55° at the surface and 15–20° at depth. The seismic profile is interpreted in terms of a structural band on the seismic section characterized by a three-layered model. The upper layer is represented by weakly discontinuous reflections that represent the overlying conglomerates. A zone of stronger reflections representing the interlayer slip fault (gold-bearing mineralized zone) is imaged within the middle of the section, while the strongest reflections are in the lower part of the section and represent metamorphic rocks at depth. At the same time, the seismic reflection survey confirms the existence of a granite body at depth, indicating that ore-forming fluids may be related to the granite. A CSAMT survey showed that the gold-bearing mineralized zone is a conductive layer and contains a low-resistivity anomaly ranging from 2 Ωm to 200 Ωm.

Notizen: A field experiment has been installed near Firebaugh in the San Joaquin Valley of California to test submergence of drains as a means of denitrification of ground water. Laboratory and field experiments have shown that denitrification occurs in saturated soil where there is ample organic carbon available for bacterial metabolism. Denitrification and dilution of high nitrate ground water were accomplished in the field.

Notizen: Environmental effects of feedlot location and related land disposal operations can be minimized if proper knowledge of hazardous conditions are known and appropriate protective steps taken. Common guidelines often do not apply because of differing physical characteristics of local areas.Analyses of various parameters within a soil profile beneath a feedlot revealed none of the chemical constituent present in high concentrations below the 23-foot depth. In areas where shallow ground water was less than 5 feet from the surface, the ground water was found to be affected by the feedlot. Other hazardous areas in feedlot location are flood-prone areas, areas of surface bedrock, and areas of excessive slope.For land disposal operations, loading rates and frequency of application of feedlot waste should be adjusted in accordance with soil permeability, depth to ground water, and irrigation practices to minimize detrimental effects on ground-water quality.

Notizen: A 2D equivalent porous media (EPM) model was used to simulate transport of tritium for a field-scale tracer experiment in a fractured and highly weathered shale saprolite. The tritium plume was characterized by rapid migration of the leading edge of the plume (up to 0.4 m/day), slower movement of the center of mass of the tritium pulse (0.009 m/day) and very slow decline of concentrations in the “tail” of the breakthrough curve (which has persisted at the site for at least 16 years). The EPM model successfully described the shape of the plume and the breakthrough curves for a monitoring well 3.7 m downgradient of the injection well using a flow velocity of 0.01 m/day and longitudinal and transverse dispersivity values of 0.8 m. An unusually low ratio of longitudinal and transverse dispersivity (αL/αT= 1) was needed to fit the nearly circular shape of the plume, which is believed to be caused by the water-table slope being perpendicular to the orientation of the prominent bedding plane fractures (which are expected to correspond to Kmax). Simulated values for concentrations in the long “tail” of the breakthrough curve observed in a downgradient well were especially sensitive to the value of longitudinal dispersivity used. The best-fit simulation, based on data over a 5 year period, was extrapolated to the most recent data point (16 years after the start of the injection) and the simulated concentration was very close to the measured value. Model predictions made with a slightly different value of longitudinal dispersivity resulted in very large errors at late time, indicating that duration of monitoring data (which strongly influences the fitting of longitudinal dispersivity) is a critical factor in accurate prediction. The experiment and simulations show that contaminant plumes can persist for long periods of time in fractured porous materials, presumably due to diffusive exchange between the rapidly moving water in the fractures and the relatively immobile pore water in the fine-grained matrix.

Notizen: The implementation of the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) may be enhanced by wider applications of vadose zone monitoring. More than 50 different vadose zone monitoring techniques are referenced. Fourteen different criteria are established for selecting alternative vadose zone monitoring methods. These monitoring methods are categorized according to premonitoring techniques, sampling methods and nonsampling methods which could be applied in the vadose zone. Two conceptual cases are presented covering vadose zone monitoring at a hazardous waste disposal impoundment. The rationale for the monitoring program at a new impoundment and for an active impoundment is presented. The material constitutes the first phase of a vadose zone monitoring manual.

Notizen: The case of E polarization of the natural electromagnetic field is analysed. The Ey(x, z) component is calculated by an iterative procedure with the conductivity ó(x, z) being set as an arbitrary function of two coordinates. The essence of the proposed 2-D inversion technique consists of correction of ó(x, z) at each step of the 2-D direct problem solution in accordance with surface admittance data. The iterative process stops when an admittance misfit reaches a given quantity. On the last iteration the accuracy of the calculated field component E(x, z) is checked. It is shown that the correction ó(x, z) at the sites x can be found through the solution 1-D linearized inverse problem with a 2-D kernel of the Fréchet differential.

Notizen: During September and October 1988 a microseismic field experiment was carried out around the city of Antofagasta, northern Chile, with 29 portable analogue and digital stations. A total of 197 reliable microearthquake locations and 19 focal mechanisms were determined. It is proposed that it is possible to estimate the maximum depth of the coupled-uncoupled transition of the subducting lithosphere using local data, defined by the depth of the expected change of the stress field from compressional to tensional along the slab. This change is observed at about 70 km depth in the Antofagasta field work. Two estimations of the width of the seismogenic interplate contact are discussed: (1) the maximum depth of the coupled zone defined by the observed maximum depth of the shallow-dipping thrust events recorded during the experiment of 47 km, corresponding to a width of the seismogenic contact zone of about 90 km; and (2) the maximum depth of the coupled zone defined by the depth of the observed change from a compressional to tensional stress field, which is 70 km and corresponds to a width of the seismogenic contact zone of about 130 km. With both values, the maximum magnitude Ms estimated for the region varies between 8.6 and 8.7. No shallow event associated with the Atacama fault system was observed during the experiment.