Ground Penetrating Radar Survey, Zimbabwe

Objective

Determining the thickness of the gravel bars and footwall topography in a pre-selected, well-formed fluvial trap-site reach.

The initial survey took 3 days and the follow up survey 1 day.

Survey Details

Line spacing was set to 100m with continuous reading along the lines. The first pass had too deep a penetration rate and resolution was lost in the thin sediments. Initially 6 targets were surveyed focused on major gravel bars and one terrace under an irrigated field. 

In order to improve resolution the antenna was changed to one for shallow penetration. This was then used for the two major  terraces. 

 GPR results overlaid on a satellite image. This gives an indication of the depth profile of the channel in context with the surroundings.

GPR results overlaid on a satellite image. This gives an indication of the depth profile of the channel in context with the surroundings.

   
  
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  The survey lines are spaced approximately 100m apart. The line traced through the centre of these lines is a section line. 

The survey lines are spaced approximately 100m apart. The line traced through the centre of these lines is a section line. 

   
  
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   Section showing depth of the channel over the survey area.

Section showing depth of the channel over the survey area.

Equipment Used

ltra-GPR made by Groundradar, very light weight – less than 4kg Specifically designed for mineral exploration using high-powered transmitters and real-time sampling receivers
Backpack mounted with tail as shown in the photographs.

Results

The initial survey was too coarse a resolution however the follow up with short penetration antenna was successful.

The second survey produced accurate sediment thicknesses finding mostly gravel. Bed rock topography was mapped to a 0.5-1m accuracy. 
Bulk sampling was then carried out at a number of localities. 

Conclusions

The survey was successful and extremely useful in a geologically complex area
Using horizontal gradient processing to enhance the continuity of structures and interpretation showing complex shear and splay structures was presented. The targets were split into primary and secondary targets depending on their potential and should all be followed up with further ground exploration such as pitting, trenching, and drilling.