Namibia enhances geophysical database

The Geological Survey of Namibia (GSN) recently began a program of geophysical activity to enhance the existing geophysical database with the aim of promoting and stimulating mineral exploration in the country.

This activity includes the reprocessing of existing data and the acquisition of high resolution airborne geophysical data over selected areas. Regional airborne geophysical surveys, with a line spacing of 1 km and a nominal flying height of 100-120 metres, have been conducted in Namibia on a more or less annual basis since 1968 and these surveys, together with reconnaissance airborne magnetic surveys conducted over the inland basins during hydrocarbon exploration, will virtually complete airborne magnetic coverage of Namibia.

These magnetic data, collected during many years and to varied specifications, have been available to the industry for some time. They have, however, been of limited use largely because much of the information was not available in digital format, and certainly not in a single compatible database.

Offering assistance is the Federal Institute of Geoscience and Natural Resources of Germany (BGR), which is providing technical co-operation in the field of geophysics to upgrade the magnetic data set, to provide a regional geophysical interpretation and to delineate areas with future exploration potential.

As a first step, Simon Petroleum Technology was contracted to compile the airborne magnetics into a single compatible database, which in part has involved the “digitizing” of some data sets.

These improved magnetic contour data are to be presented in both black and white, and color, at a scale of 1:1 million and in a 1:250,000 map series comprising 39 sheets. The data will also be available as digital grids conforming to the 1:50,000, 1:250,000 and 1:1 million topographic map series. In addition to the magnetic data, most of the regional geophysical surveys conducted by the government included radiometrics; the data are even more diverse in nature than the magnetics, with variations in crystal volume adding to the complexity of any compilation.

As a test, the GSN and BGR have selected an area covering four 1:250,000 scale topographic maps to compile radiometric data obtained from 11 surveys conducted between 1968 and 1980. The process has involved the digitizing of analogue records for those surveys not recorded digitally and the subsequent back calibration of the radiometric systems by conducting ground surveys over selected areas prior to the reprocessing of the radiometric data. This work is being undertaken by DMT-Institute of Applied Geophysics in Germany and Uruhart Dvorak of Canada, and early results have encouraged GSN and BGR sufficiently to plan for a compilation of the complete Namibian radiometric data set.

In addition to upgrading the existing airborne geophysical data, the GSN is planning to upgrade its geophysical database by executing surveys with closer line spacing and more demanding specifications incorporating recent advances in data acquisition and processing.

The first phase of this program of high resolution surveys will commence this year and will be financed through the European Community (SYSMIN) within the framework of a support program to the mining sector of Namibia. The long-term aim is to provide high resolution airborne magnetic and radiometric data of the whole country.

This upgrading will be achieved initially by conducting surveys over selected areas which have an increased potential for economic discoveries, and then by selling the data, at a fraction of acquisition cost and on a non-exclusive basis, to mining companies.

The revenue from data sales will accrue to a revolving fund established by government to provide funds for the development of the mining industry, including future airborne geophysical surveys.

For more information, contact the Geological Survey of Namibia, Box 2168, Windhoek, Namibia.