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Geophysical mapping in Archean greenstone belts of Tanzania as an aid for gold prospecting
SITE INVESTIGATIONS:BQREHOLES
3IBA
967160 Experience in using geophysical methods for reconstructing hydraulic structures in cities A. S. Aleshin, A. D. Zhigalin, G. M. Kaganov, V. I. Volkov & I. S. Rumyantsev, Hydrotechnical Construction, 29(5), 1995, pp 283-286; translated from: Gidrotekhnicheskoe Stroitel’stvo, 5, 1995, pp 16-19. Investigations have demonstrated the effectiveness of using geophysical methods for solving hydrotechnical problems under a hieh level of industrial noise and limited free territory. Thee presence of a buttress wall in the stratum of made ground was established and its extent was determined by means of the resistivity method. The use of the SP method in the ground surface and water variants in combination with observations by the biolocation method made it possible to detect the existence of bypass seepage and to establish the places of seepage and discharge of subsurface streams. It was shown, in particular, the bypass seepage is concentrated mainly in the stretch of abutment of the Borisovsk dam against the waste canal. Other less significant seepage flows also discharge in the channel of the discharge canal. (from Journal summary)
967164 Integrated geophysical study of the the southern part of Nisyros Island, E. Lagios & G. Apostolopoulos, ~o~r~~~ of Applied Geophysics, 34(l), 1995, pp 55-61. The study of the high-enthalpy geothermal field of Nisyros Island is of great importance, because construction of a geothermal power station. the applied geophysical surveys - gravity, SP, VLF and audiomagnetotelluric - in southernmost Nisyros was to investigate the major and minor faulting zones which are geothermally active, i.e. whether geothermal fluid circulation occurs in these zones. The geothermal fluid ci~cn~atio~ zones, detected by the SP method, appear to be well correlated with corresponding features derived from the gravity and the AMT surveys. In particular, the AMT soundings indicate two zones of geothermal fluid circulation instead of the one the SP method detected in the central part of the investigated area. (from Authors)
967161 The search for water goes beyond intuition C. E. Nuzman & C. Kinn, International Ground Water Technology, l(9), 1995, pp 23-24,26-30. The use of geophysical methods to supplement test drilling and help determine the best available location and depth for the construction of a water supply well is described. Geophysical surface techniques can also be used as a nonintrusive survey method in environmental applications for locating buried drums or delineating contaminant plumes and landfill boundaries. Geophysical methods available are described including electrical methods, seismic techniques, gravity methods, magnetic and electromagnetic methods, ground penetrating radar, geothermal tech;ques, magnetotellurics and test hole drilling. A case study is given describing the use of geothermal methods to locate a fractured dolomite aquifer. (P.M.Taylor)
967165 Geophysical mapping in Tanzania as an aid for gold D. G. Eberle, First Break, 1 The worldwide acceleration in gold exploration activity has created a demand for improved geophysical prospecting procedures to complement the growing knowledge of the geochemistry of gold and its distribution in the Earth’s crust. Gold mineralization in Archean granite-~ree~st~ne terranes contributes about 15% of the world’s gold production presently amounting to approximately 1300 metric tonnes (t) per year. There is no geophysical respecting tool which can detect gold directly. The gold content of the rock in an ore body is so small that only indirect geophysical prospecting techniques can be applied. Greenstone belts are known to be confined to Archean shields. Many of them are situated in tropical and semi-to fully arid terrains, where weathering is severe. Especially under these conditions, ~ul~~phase geophysical mapping will provide detailed knowledge of the geological setting, thus providing to be a powerful tool for use in gold prospecting. (from Author)
967162 Thermal neutron logging monitors solvents A. L. Endres & .I. P. Greenhouse, International Ground Water Technology, l(9), 1995, pp 13-14,16-18. The use of thermal neutron logging to monitor solvents through an aquifer is described. Neutron logging is a geophysical tool for mapping variations in the water content of a formation. The contamination of aquifers by immiscible organic liquids is a serious environmental problem. If the predominant chlorine source in an aquifer is a chlorinated solvent, observed changes in the response of thermal neutron devices can be related to the amount of solvent present. Results of a field experiment with perchloroethylene are presented and discussed. (P.M.Taylor) 967163 Application of aeromagnetic data to mineral potential evaluation in Minnesota A. Spector & T. L. Lawler, Geophysics, 60(6), 1995, pp 17041714. Aeromagnetic, ground magnetic, and gravity data, together with all available drillhole data and physical property measurements, were used to map the Precambrian geology of an area in Minnesota that is virtually devoid of outcrop. The work was done for purposes of land use planning and to encourage minerals exploration and mostly consisted of the analysis of profiles of aeromagnetic data to map magnetic/ lithologic contacts, to infer structure, and to determine thickness of overburden cover. Thirty-seven sites were resolved from the aeromagnetic data as targets for base metal sulfide (copper, zinc) as well as precious metal (gold) mineralization. Thirteen magnetic anomalies were identified as possible kimberlite pipes. (from Authors)
Bosehole an
967166 Bohrlochradar - ~r~ndlagen und A~~~~ tein (Borehole-radar - principle and a masses) L. Corin, B. De&y, L. Nalleux & ichter, _Wsbsbau,13(5), 1995, pp 285-290. The application of high-frequency electro~~~n~t~c methods in the Mhz-range from boreholes is one of the latest and most sophisticated process developments in applied geophysics. Starting with basic principles of the process, the method of unidirectional and directional reflection (single hole) and tomographic measurements (cross hole) are explained. With the help of two selected geotechnical largescale projects in the course of the European traffk-route 6~~$tr~~tion (highspeed-train Cologne-Brussels-Paris: tunnel of Soumagne, viaduct of Arbre) the methodical and inte and the performance of these special methods for foundation investigations are demonstrated. (from English summary)
3IBA
967160 Experience in using geophysical methods for reconstructing hydraulic structures in cities A. S. Aleshin, A. D. Zhigalin, G. M. Kaganov, V. I. Volkov & I. S. Rumyantsev, Hydrotechnical Construction, 29(5), 1995, pp 283-286; translated from: Gidrotekhnicheskoe Stroitel’stvo, 5, 1995, pp 16-19. Investigations have demonstrated the effectiveness of using geophysical methods for solving hydrotechnical problems under a hieh level of industrial noise and limited free territory. Thee presence of a buttress wall in the stratum of made ground was established and its extent was determined by means of the resistivity method. The use of the SP method in the ground surface and water variants in combination with observations by the biolocation method made it possible to detect the existence of bypass seepage and to establish the places of seepage and discharge of subsurface streams. It was shown, in particular, the bypass seepage is concentrated mainly in the stretch of abutment of the Borisovsk dam against the waste canal. Other less significant seepage flows also discharge in the channel of the discharge canal. (from Journal summary)
967164 Integrated geophysical study of the the southern part of Nisyros Island, E. Lagios & G. Apostolopoulos, ~o~r~~~ of Applied Geophysics, 34(l), 1995, pp 55-61. The study of the high-enthalpy geothermal field of Nisyros Island is of great importance, because construction of a geothermal power station. the applied geophysical surveys - gravity, SP, VLF and audiomagnetotelluric - in southernmost Nisyros was to investigate the major and minor faulting zones which are geothermally active, i.e. whether geothermal fluid circulation occurs in these zones. The geothermal fluid ci~cn~atio~ zones, detected by the SP method, appear to be well correlated with corresponding features derived from the gravity and the AMT surveys. In particular, the AMT soundings indicate two zones of geothermal fluid circulation instead of the one the SP method detected in the central part of the investigated area. (from Authors)
967161 The search for water goes beyond intuition C. E. Nuzman & C. Kinn, International Ground Water Technology, l(9), 1995, pp 23-24,26-30. The use of geophysical methods to supplement test drilling and help determine the best available location and depth for the construction of a water supply well is described. Geophysical surface techniques can also be used as a nonintrusive survey method in environmental applications for locating buried drums or delineating contaminant plumes and landfill boundaries. Geophysical methods available are described including electrical methods, seismic techniques, gravity methods, magnetic and electromagnetic methods, ground penetrating radar, geothermal tech;ques, magnetotellurics and test hole drilling. A case study is given describing the use of geothermal methods to locate a fractured dolomite aquifer. (P.M.Taylor)
967165 Geophysical mapping in Tanzania as an aid for gold D. G. Eberle, First Break, 1 The worldwide acceleration in gold exploration activity has created a demand for improved geophysical prospecting procedures to complement the growing knowledge of the geochemistry of gold and its distribution in the Earth’s crust. Gold mineralization in Archean granite-~ree~st~ne terranes contributes about 15% of the world’s gold production presently amounting to approximately 1300 metric tonnes (t) per year. There is no geophysical respecting tool which can detect gold directly. The gold content of the rock in an ore body is so small that only indirect geophysical prospecting techniques can be applied. Greenstone belts are known to be confined to Archean shields. Many of them are situated in tropical and semi-to fully arid terrains, where weathering is severe. Especially under these conditions, ~ul~~phase geophysical mapping will provide detailed knowledge of the geological setting, thus providing to be a powerful tool for use in gold prospecting. (from Author)
967162 Thermal neutron logging monitors solvents A. L. Endres & .I. P. Greenhouse, International Ground Water Technology, l(9), 1995, pp 13-14,16-18. The use of thermal neutron logging to monitor solvents through an aquifer is described. Neutron logging is a geophysical tool for mapping variations in the water content of a formation. The contamination of aquifers by immiscible organic liquids is a serious environmental problem. If the predominant chlorine source in an aquifer is a chlorinated solvent, observed changes in the response of thermal neutron devices can be related to the amount of solvent present. Results of a field experiment with perchloroethylene are presented and discussed. (P.M.Taylor) 967163 Application of aeromagnetic data to mineral potential evaluation in Minnesota A. Spector & T. L. Lawler, Geophysics, 60(6), 1995, pp 17041714. Aeromagnetic, ground magnetic, and gravity data, together with all available drillhole data and physical property measurements, were used to map the Precambrian geology of an area in Minnesota that is virtually devoid of outcrop. The work was done for purposes of land use planning and to encourage minerals exploration and mostly consisted of the analysis of profiles of aeromagnetic data to map magnetic/ lithologic contacts, to infer structure, and to determine thickness of overburden cover. Thirty-seven sites were resolved from the aeromagnetic data as targets for base metal sulfide (copper, zinc) as well as precious metal (gold) mineralization. Thirteen magnetic anomalies were identified as possible kimberlite pipes. (from Authors)
Bosehole an
967166 Bohrlochradar - ~r~ndlagen und A~~~~ tein (Borehole-radar - principle and a masses) L. Corin, B. De&y, L. Nalleux & ichter, _Wsbsbau,13(5), 1995, pp 285-290. The application of high-frequency electro~~~n~t~c methods in the Mhz-range from boreholes is one of the latest and most sophisticated process developments in applied geophysics. Starting with basic principles of the process, the method of unidirectional and directional reflection (single hole) and tomographic measurements (cross hole) are explained. With the help of two selected geotechnical largescale projects in the course of the European traffk-route 6~~$tr~~tion (highspeed-train Cologne-Brussels-Paris: tunnel of Soumagne, viaduct of Arbre) the methodical and inte and the performance of these special methods for foundation investigations are demonstrated. (from English summary)