The new magnetic data set of Namibia and its significance for crustal research and mineral prospecting

Abstract

varied but were largely the result of insufficient qualified manpower within the Geological Survey 41 airborne magnetic surveys flown between 1962 and and perhaps, more importantly, the diverse nature 1992 over different areas of Namibia have been comof the data themselves. piled as part of a German-Namibian technical cooperation project to produce a refined compatible MAGNETIC FIELD DATA national (countrywide) magnetic data set. Final maps are available in two scales (1 : 1,000,000; The magnetic data derived from 41 different survey 1 : 250,000) with digital grids produced using blocks (Fig. 1) were collected to varying specifithree different cell sizes (2000 m, 500 m, 200 m). cations using different magnetometers with varying surveys parameters and were presented as contour These refined magnetic data sets are serving as a maps with varying reference levels and in most new tool to elucidate the evolution of the crust cases the International Geomagnetic Reference and to re-assess the mineral potential of Namibia : Field (IGRF) was not removed. These airborne (1) Distinctively different magnetic patterns can magnetic data though on open file for many years be observed over cratonic shield areas and were therefore not available as a single compatiproterozoic mobile belts, the latter characteble data set and were thus not conducive to rised by very well defined magnetic and nonregional interpretation. magnetic zones. Paleozoic and mesozoic units generally show a strong magnetic response. DATA COMPILATION (2) Analysis of magnetic linear features reveals the existence of two directional sets of In an effort to overcome the problems inherent to magnetic lineations running across both mobile such a heterogeneous data set, the German Federal belts and shield areas. Institute of Geoscience and Natural Resource (BGR) (3) Evaluation of the magnetic signature over has been providing technical assistance to the known mineral deposits encourages the identiGeological Survey of Namibia (GSN). The main aims fication of very similar signatures in underare to upgrade the Namibian magnetic data, to explored portions of the country, such as the provide regional geophysical interpretation sand-covered Kalahari and Namib deserts. including ground truth control and to delineate areas with future mineral exploration potential. INTRODUCTION At the start of the program, Simon Petroleum TechDespite regional airborne geophysical surveys nology Ltd. (SPT) were contracted to merge the having been conducted in Namibia since 1962 and airborne magnetic data into a single uniform comthat these surveys, together with reconnaissance patible data base, and the following steps were magnetic surveys conducted over the inland basins undertaken to achieve this objective : during hydrocarbon prospecting, almost completely cover the entire country, very limited regional i) Determination of the original absolute field interpretation of these data has been undertaken, values for each survey. and very little (Corner, 1983) has been published ii) Calculation of the IGRF model (IAGA, 1986) to date. The reasons for this are historic and for the survey date.