Methodology
Hummingbird is focused on thorough and systematic exploration within sensible economic parameter and timeframes. Hummingbird’s exploratory methodology in Liberia may vary slightly between different concession areas, but broadly follows the exploration sequence below:
Geological MappingFor those areas which are judged to be anomalous, follow up work will continue in the next field season in a systematically evolving manner. Additional stream sediment sampling is undertaken where the first season's sampling has established anomalous values and continues with further samples upstream from those points. The aim of the sampling is to more closely identify the sources of the anomalous heavy mineral accumulations in the stream.
Stream Sediment SamplesThe sampling programme concentrates on obtaining heavy sediment samples from the drainage courses, with particular emphasis on second and third order drainages (this is because the first order streams are too full of water, even in the dry season, to be safe or practicable to sample). Large samples (40 litre, or >50 kg) are taken on each site and sieved and jigged down to form a heavy mineral concentrate of 1-2 kg. GPS coordinates of sample points, and the presence of heavy mineral grains and evidence of artisanal diggings are observed and noted for each site. Overall sample density should be 0.5-1 samples per square kilometre

The concentrate samples are taken to Monrovia and first sieved and split down to a sample of approx 50g each at the Alex Stewart prep lab in Monrovia. These samples are then air-freighted to the OMAC laboratory in Ireland for the following analyses:

  • Homogenisation of sample followed by standard Au geochem analysis, including pre-ignition at 6500 C.
  • Aqua regia digestion followed by ICP - AR / ES 46 element scan, which included rare earths (eg. Ce, La, Th, Y, V), base metals and other indicators (including Cu, Pb, Zn, As, Ba, Fe, Cr, Mn, Sr), and other heavy minerals (eg. Ti, Zr).
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Additional stream sediment samplingFor those areas which are judged to be anomalous, follow up work will continue in the next field season in a systematically evolving manner. Additional stream sediment sampling is undertaken where the first season's sampling has established anomalous values and continues with further samples upstream from those points. The aim of the sampling is to more closely identify the sources of the anomalous heavy mineral accumulations in the stream.
Air-photo and satellite workThis work is conducted over anomalous areas identified in the first phase of stream sediment sampling work. Existing Satellite DTM is complemented with Landsat and other satellite imagery, as well as aerial photography (if available).
Soil geochemical workOnce the stream has been followed upstream to where there are no more anomalous heavy mineral accumulations, it is because the source of the minerals in the stream banks has been passed. At this stage the search focuses on 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 is to establish unambiguous anomalies of heavy minerals at surface in the soil.
Trenching The above soil geochemical work hopefully outlines anomalous zones of minerals on the surface of the soil. The purpose of the trenching programme is 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 can then be geologically mapped and sampled with channel samples. The aim of this work is 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.
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Drilling Once the source of the soil anomalies had been established in the bedrock, the aim of the first stage of drilling is 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 (vein / shear related gold deposits), diamond core drilling is favored 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 require a relatively high level of geological input.
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