Geophysics Division


Geophysics is one of six operational divisions within the Geological Survey of Namibia. The Division is responsible for the acquisition and interpretation of geophysical data for the mineral exploration sector and research institutions. The Geophysics Division consists of three subdivisions namely Airborne Geophysics, Ground Geophysics and Interpretation Geophysics.
Geophysics Division Sub-Divisions
Airborne Geophysics Responsible for all aspects of airborne geophysical surveys including survey planning and specifications, tender evaluation and award, contract supervision and quality control, data processing, data management and sales. In addition to the Regional Airborne magnetic data set, a national programme of high resolution magnetics and radiometrics is nearing completion, and other airborne surveys undertaken in recent years include electromagnetics, hyperspectral scanning and gravity.
Regional Airborne Geophysical Data During a thirty year period nearly all of Namibia was gradually covered by regional airborne geophysical (magnetic and radiometric) surveys with typical 1000-m line spacing and a ground clearance between 100 and 150 m.
Magnetics Some 41 different surveys flown between 1962 and 1992 were homogenised and merged within the framework of technical co-operation between the Geological Survey of Namibia and the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany. Data are available as whole area grids with 2000 m, 500 m and 200 m cell size and scissored according to the Namibian Map System in 1:250.000 map sheets (500 m cell size) and 1:50.000 map sheets (200 m cell size).	Click on image for a 151Kb image of regional airborne magnetic map with links to 1:250 000 regional magnetic map sheets
Radiometrics Within the framework of technical co-operation between the Geological Survey of Namibia and the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany, data were back-calibrated covering an area of 11 1:250.000 map sheets. To merge different surveys of varying quality, the data had to be back-calibrated using ground control points. Counts per second were transferred into ground concentrations of the three radioactive elements Potassium, Uranium, Thorium and into Exposure Rate (Total Counts) using calibrated hand held 256 channel spectrometers. These data are available in gridded format scissored according to the Namibian Map System as 1:250.000 map sheets with 250-m grid cell size	Click on image for a 94Kb image of regional airborne radiometrics map with links to highlighted 1:250 000 regional magnetic map sheets
High Resolution Airborne Geophysical Programme The programme of High Resolution Airborne Geophysical surveys comprising of 200 m line spacing and a ground clearance of 80 m to 100 m started in 1994. Data acquired included magnetic and radiometric and to date over 4.4 million line-kilometers of data are available with a complete national coverage at 97 %. Digital data are available in gridded format and as located line data to allow customized tailored reprocessing and line data interpretation. These data are sold at rate of N$1 per line km for the complete data set or N$ 0.5 per line km for gridded data only. Other products are available such as Geotiffs and further information can be obtained by contacting the Geological Survey.
High Resolution Airborne Index
Radiometric Calibration Facilities Radiometric surveys have become increasingly important for mineral exploration and environmental studies, especially since data quality is improved by modern spectral processing. The calibration of airborne and ground instruments, making use of calibration pads and a Dynamic Calibration Range, is essential to achieve comparable results in units of ground concentration. Calibration pads are available at the Eros Airport close to the Geological Survey in Windhoek. The Dynamic Calibration Range is situated close to Henties Bay at the central Namibian coast. The area meets the criteria defined by the International Atomic Energy Agency (IAEA) in 1991. The range consists of a flat 2 x 11 km wide area stretching approximately 1 km inland along the coast, that was surveyed on a 100 x 100 m grid using calibrated hand held instruments. A nearby airstrip and the airport of Swakopmund, 60 km to the south, complete the facilities. Digital data and hardcopy maps of the Dynamic Calibration Range can be made available to all interested parties.
Airborne Gravity In 2004, a GT-1A airborne gravity test survey flown at 80m AGL was conducted by GPX Survey in the Rehoboth, Grootfontein and Bushmen areas. The acquired data was processed but yet to be interpreted. The respective datasets from these survey areas are available at the GSN in a Geosoft format.
Airborne Electromagnetic In June -July 2005, Fugro Airborne Surveys undertook an airborne TEMPEST electromagnetic and magnetic survey over the Eiseb area in Northern Namibia. The surveys consist of one test lines and two survey blocks. Following the success of the TEMPEST survey, in June 2008, a Helicopter-borne VTEM survey was flown by GEOTECH AIRBORNE Ltd in the Maroelaboom area. The data was processed and a preliminary interpretation was carried out with several proposed mineralization zones being identified. Subsequently to that, two more surveys were flown in the Erongo region mainly; Trekkopie and Lofdal surveys. However, the final data on these surveys' are yet to be processed.	Airborne EM helicopter flown over Lofdal and Trekkopie area
Hyperspectral Hyperspectral survey were conducted as from 2004 and the covered areas are Otavi, Sikereti, Mowe Bay, Erongo region, Erindi, Navachab, and Rehoboth as it can be seen in the Fig. 5. With this tool you can map out alterations minerals for exploration purpose.
Colour composite of false image and the bands are 28, 15 and 03 at Langer Heinrich Uranium mine	Mica abundance and Kaolinite at Langer Heinrich Uranium mine
HyMap images of Langer Heinrich uranium mine area
Ground Geophysics Responsible for all ground geophysical surveys conducted by government as well as the monitoring of earthquakes, the operation and maintenance of a national seismological network and the operation of the Tsumeb International Monitoring Station (auxiliary seismics and Infrasound) on behalf of the Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO).
Gravity More than 13.000 gravity stations are currently held by the Geological Survey. To improve data density a gravity programme will be launched in the near future aiming at coverage of one gravity station per 10 km2. The network stations will be linked to a base station that is in turn connected to four absolute gravity stations established by NIMA in 1997. With the purchasing of new gravity-meter (CG-5), this national project will improve regional gravity coverage.	Click on image for a 108Kb image of regional gravity map.
Magnetotelluric A Magnetotelluric survey was conducted by Southern African MagnetoTelluric EXperiment (SAMTEX). The programme aimed to study the cratonic boundaries of Southern Africa and provide information about lithospheric strike directions and the resistivity distributions as well as possible locations of terrane boundaries.	Landsat TM5 image of parts of the Kaoko Region (North-Western Namibia)
Resistivity Survey A resistivity survey in the Tsumeb area was conducted as collaboration between the Geological Survey and the Federal Institute for Geosciences and Natural Resources (BGR, Germany). The aim was to establish and locate a new waste dumpsite for the town as the pre-existing site was leaching contaminates into the groundwater system.
(Left) Surfer-Classed- Post map of resistivity distribution and (Right) Sketch of a complete apparent resistivity pseudo-map, which shows a remarkable a-symmetric distribution of the low resistivity zones within the western syncline. Black crosses indicate the survey lines.
Tsumeb Geophysical Research Station The Tsumeb Station monitors seismic activity as part of the Global Seismological Network (GSN), funded and operated by the Incorporated Research Institutions for Seismology (IRIS - a consortium of 80 universities in the USA) in co-operation with the United States Geological Survey (USGS). A second station will be established in Windhoek shortly. Other joint research ventures include monitoring magnetic secular variation in co-operation with the Hermanus Observatory, South Africa and neutron emissions in conjunction with the University of Potchefstroom, South Africa.
Seismology Six seismological stations (Windhoek, Tsumeb, Rundu, Kamanjab, Aus and Ariamsvlei) form the National Seismological Network. The network records earthquakes countrywide and provide data for the Earthquake Hazard Map of Namibia. The Tsumeb station is also part of the Global seismological Network and Incorporated Research Institutions for Seismology (GSN/IRIS) and the station contributes to worldwide earthquake monitoring. It is also one of the Comprehensive Nuclear-test-Ban Treaty Organizations (CTBTO), International Monitoring Stations (IMS) AS067 monitoring nuclear explosions worldwide. Three more seismological stations are planned for next year at Opuwo, Arandis and Gobabis. The seismic areas in the country are along the Waterberg thrust, the Windhoek graben, the Sesfontein graben and the Kuboos-Bremen line of intrusive crossing the border into South Africa. Some of the seismic events recorded have been catalogued and depicted below on the geological map of Namibia.(map) The portable seismological stations have also been purchased and will be deployed along faults/trusts and in some towns to determine seismogenic faults, site effects and ground amplification for seismic micro-zonation mapping.
Seismic events in Namibia recorded over the last 100 years; size of circle indicates magnitude of event.
Interpretation Geophysics This newly created subdivision was established following the success of the BRGM (French Geological Survey) SYSMIN funded interpretation project. Once fully staffed the Interpretation unit will provide complementary interpretation services to airborne and ground geophysics, and will work closely with other divisions within the Geological Survey to provide quality geological interpretations of geophysical and remote sensing data.
Interpretation Geophysics Sub-Divisions
Magnetics work still in progress
Electromagnetic An airborne electromagnetic interpretation workshop was conducted by Fugro Airborne Surveys on the Eiseb project (Area 2 and 3) early this year. The integrated interpretation was mainly on the Tempest AEM and Regional magnetic data. However, a comprehensive report on the interpretation was never delivered but various deliveries of grids plus power presentations on the workshop were received
Results of Area 2 and 3 that formed part of the AEM interpretation.
Hyperspectral Work still in progress