Interpretation of Aerogeophysical Data Supporting the Mineral Assessment of the Kirk Range Area, Republic of Malawi

EM-Survey, Kirk Range Area Source: BGR

A mineral assessment study was executed in 1997 within the framework of Technical Cooperation between the Governments of the Republic of Malawi and the Federal Republic of Germany in the field of geoscience. Partners of this cooperation are the Geological Survey Department of Malawi, Zomba, and the Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany.

The study concentrated on the possibility of economic mineral deposits occurring in the Kirk Range, which is believed to be a promising target for prospecting activities. With this in mind, new methods were applied, in particular geophysics using modern evaluation software, and remote sensing with emphasis on satellite image interpretation. In addition, all available data, e.g. on geology and geochemistry, were included in the considerations. The main aim was a general assessment of the mineral potential of this region.

Use of new processing software allowed a better visualisation and improved interpretation of geophysical data and, in this way, lead to better understanding of aerogeophysical anomalies. The discovery of meta-igneous rocks in the Kirk Range, mainly laminated granites and granite gneisses, via satellite images and their confirmation by geological field work and geophysics provided us with new ideas about the hydrothermal events in the study area, leading to new genetic concept for gold mineralisation.

This mineral assessment has not revealed any spectacular new discoveries. However, after thorough discussion on the basis of the current state of knowledge, recommendations were made with respect to gold and rock phosphate, as well as on bauxite and kaolonitic clay. Further, it was recommended that a few electromagnetic anomalies, which have not yet been checked in the field be examined. These EM anomalies may be associated with sulphidic mineralisations.

The most spectacular geophysical anomalies in the survey area is caused by igneous rocks of the Mlindi circular structure. This biotite pyroxenite intrusion with a size of about 6 to 8 km is characterised by an elevated apatite content. This mineral can be used as a rock phosphate fertilizer.

The graphs below show geophysical anomalies from the nation wide airborne magnetic, spectrometer and in some parts electromagnetic surveys. Line spacing in this detailed Mlindi area was 250 meters and terrain clearance 120 meters.