Ground Magnetics In The Zambezi Rift, Basin Analysis Heavy Mineral Exploration, Zimbabwe

Objective

Mapping any obvious geological structures which might influence the drainages and create trap sites for alluvial concentrations of heavy minerals. 

The area is covered with poorly consolidated Cretaceous sediments of unknown thickness, and wide, shallow, braided streams cut through the area

 Total field magnetics from the North Block survey with interpretation overlaid. A number of shallow NW-trending linear structures are evident which may be of importance. The outline of a deep-seated basement feature is also shown.

Total field magnetics from the North Block survey with interpretation overlaid. A number of shallow NW-trending linear structures are evident which may be of importance. The outline of a deep-seated basement feature is also shown.

 1VD of the ground magnetics with interpretation overlaid. Only the NW structures show.

1VD of the ground magnetics with interpretation overlaid. Only the NW structures show.

 South Block total field with interpretation overlaid. The thick black lines represent dykes, or layers, whilst the interpreted structures are shown in dashed line. The small, spikey anomalies in the centre of the survey are caused by houses and sheds within a village.

South Block total field with interpretation overlaid. The thick black lines represent dykes, or layers, whilst the interpreted structures are shown in dashed line. The small, spikey anomalies in the centre of the survey are caused by houses and sheds within a village.

 South Block 1VD with interpretation overlaid. The thick black lines represent dykes, or layers, whilst the interpreted structures are shown in dashed line. The numerous small anomalies in the centre of the survey are within a village.

South Block 1VD with interpretation overlaid. The thick black lines represent dykes, or layers, whilst the interpreted structures are shown in dashed line. The numerous small anomalies in the centre of the survey are within a village.

Survey Details

The two survey areas measured 1.3 km x 2 km (North Block) and 4km x 2km (South Block). The survey was planned with 100m spaced north-south lines and a 20m station spacing. 

Equipment Used

The survey was completed using GEM’s GSM-19 (Overhauser) Magnetometer Derivatives and analytical signal calculated in Oasis Montaj.

Data Processing and Quality

Good quality data was collected, and the diurnal variation has been properly removed. The data were gridded as total field data and the derivatives and analytical signal calculated in Oasis Montaj. Ground survey results matched up well to the regional aeromagnetics, showing ground to air correlation were good. 

Interpretational Work

The total field magnetics for the northern block showed very little except for a broad magnetic high interpreted as a large basement feature, and a number of shallower NW-trending structures. These structures may be of importance in terms of alluvial trap sites.
The South Block results display a very well-defined multiple E-W dyke system in the south of the survey area, or else they are possibly layers within a complex lithology. To the immediate north of this are a number of small, spikey anomalies that appear to be culturally related, as there are numerous house and sheds in a village here. In addition there are a number of subtle NW-trending structures, similar to those in the North Block. The multiple dykes, or layers, and structures will almost certainly create good trap-sites in streams on surface. The dykes, or layers, have been truncated and disturbed by the NW structures in places. Aside from these features in the magnetics, there is little else. The northern half of the survey area is very quiet except for a few very subtle NW structures, which appear to be controlling the drainages here.

Conclusions

The survey achieved the objective of mapping geological and structural features within the area. Some of the structures have shown possible alluvial trap sites.