On those areas which are judged to be anomalous, follow up work will continue in the next field season in a systematically evolving manner, using a combination of the following techniques as required:
Additional stream sediment sampling
This will begin where the first season’s sampling has established anomalous values and continue with further samples upstream from those points. The aim of the sampling will be to more closely identify the area causing the anomalous gold / diamond / indicator values in the stream.
Airphoto and satellite work
This work will be conducted over anomalous areas identified in the first phase of stream sediment sampling work. Satellite DTM work has already been used and this will be complemented with Landsat and other satellite imagery, as well as aerial photography (if available). Based on the results of the first year’s work on the Hummingbird projects, the following methodologies are likely to be considered for the field work for the second and third years, in approximate sequential order. The priority is to identify anomalous target zones within the Hummingbird project areas in as short a period of time as possible.
Stream sediment geochemical sampling
This would essentially be follow-up work from the first year’s work. It would concentrate on areas of favourable results and take further heavy mineral samples upstream of the anomalous values discovered during the first field season. The aim of the work would be to establish the sources of the anomalous heavy mineral accumulations in the stream sediments.
Soil geochemical work
Once the stream has been followed upstream to where there are no more anomalous heavy mineral accumulations, it is because the source of the minerals (eg. gold, diamonds, diamond indicator minerals) in the stream banks has been passed. At this stage the search would focus onto the stream banks or spurs between the streams, with systematic soil samples in grids to further determine the source of the heavy minerals. The aim of the soil geochemical work would be to establish unambiguous anomalies of heavy minerals at surface in the soil.
Trenching
The above soil geochem work will hopefully outline anomalous zones of minerals on the surface of the soil. The purpose of the trenching programme would then be to try to establish the true source of those soil anomalies, below the soil in the top of the bedrock. Trenching can be conducted manually or with mechanical diggers. Provided the soil depths are not prohibitively deep (say 5 to 7 m or less), the trench should expose the top of the bedrock, which could then be geologically mapped and sampled with channel samples. The aim of this work would be to establish, for the first time, a width and grade of a mineralised body in the bedrock. However, it should be stressed that at trenching depths in deeply weathered terrains such as in Liberia, the bedrock can be expected to be strongly weathered and quite possibly depleted in terms of mineralisation.
Drilling
Once the source of the soil anomalies had been established in the bedrock, the aim of the first stage of drilling would be to ascertain down-dip continuity of the mineralised features, with specific emphasis on obtaining fresh samples of the mineralised deposit. For the likely types of deposits in mind (eg. kimberliterelated diamonds, or vein / shear related gold deposits), diamond core drilling would be favoured over destructive methods such as RC or RAB drilling, in that the former, while more expensive, is able to obtain far greater precision in terms of geology, sampling etc. The above types of mineral deposits are usually structurally controlled and therefore complex, so would require a relatively high level of geological input.
Geological mapping
This activity would be undertaken at different scales. The broad anomalous areas would be studied with detailed satellite imagery and air photos (where available). This work would obtain greater detail regarding the geology and topography of the area in question, in order to help interpret the sampling results. In addition to this, ground traverses would be undertaken to observe and record any visible geology in the area of interest. On a more detailed scale the trenches will be geologically logged.
Ground geophysics
After heavy mineral (eg. gold / diamond / indicator) anomalies have been defined in the soils, ground geophysics is an important tool to define them further. An example is ground magnetics – in the case of a kimberlite dyke / pipe, the ultramafic body itself generally shows as a magnetic anomaly, while in the case of shear-hosted gold, the fault structures normally show up as magnetic discontinuities. The normal method is to run hand-held magnetometer surveys along the soil sampling lines across the anomaly in question.