Pitting & Trenching
A series of pits are generally excavated across contiguous soil anomalies to identify the source of mineralization at depth. Pits are roughly 1m x 1m and manually excavated to bedrock if feasible. Once completed pits must be mapped and channel samples must be collected in bedrock/saprolite at the base of each pit. Samples must be collected from a 5cm wide and 3cm deep slot 10cm above the base of the pit and should not exceed 3kg wherepossible.
Trench sampling is carried out by channelling a sample along the trench of the floor. Each channel will be approximately 10 centimetres wide and 3 to 5 centimetres deep. Sampling is carried out “geologically” i.e. sample intervals were determined by geological features, and not done simply on a meter by meter basis. In homogeneous rock, the maximum sample interval shall be 1 metre. The minimum sample interval employed is 0.3 m. Veins, altered zones, or distinct geological units will be sampled so that the contacts were a standard 2 cm within the sample boundaries. Sample weights are recorded and vary between 3 kilogram and 6 kilogram. Channel sample methodology is similar to that described for trenches above. A total of about 1,000 metres of trenches will be excavated and 1100 trench samples will be collected. Channel samples must be collected from the base of each pit:
- where no obvious mineralised structure is identified a channel sample must be collected from two adjacent walls as shown in Figure and a second sample from the remaining adjacent walls.
- Where a mineralized structure is evident at the base of the pit a channel sample must be collected across the structure as shown in Figure
- Separate ticket books with a separate range of ticket numbers are to be used for all pit samples
- Samples must be collected in plastic bags with the unique ticket number folded and stapled into a fold at the top of the bag
Once the zone of mineralization has been identified, a trench will be excavated across the mineralized structure/s. The trench must be extended to cover at least 5m on either side of the mineralized zone to ensure coverage of potentially mineralized structures in the footwall and hanging wall rocks. All trenches are to be logged in detail by the geologist. Beginning and end coordinates of each trench, rock type, quartz veins, lithological boundaries, structural measurements, visible mineralization and sample intervals are to be recorded on the appropriate data collection sheet. Channel samples are to be collected from a 5cm wide and 3cm deep slot 10cm above the base of the trench:
- Channel samples must have a maximum length of 2m and a minimum length of 30cm and should not exceed 3kg
- A sample across a mineralized vein or shear should continue for 2cm on either side of the unit
- Samples should not cross lithological boundaries
- Special care must be taken to ensure a representative sample is collected (tendency is to have more soft material and less hard material which is not representative of the grade and will often dilute overall grade if mineralisation is focused in hard quartz veins).
- Separate ticket books with a separate range of ticket numbers are to be used for trench samples
- Samples must be collected in plastic bags with the unique ticket number folded and stapled into a fold at the top of the bag.
At the end of every day all pit and trench samples are to be prepared for dispatch at camp (permanent or temporary):
- A maximum of 10 x 2-3kg samples are to be stored in white polyweave bags ready for dispatch to the laboratory. These must include standards, blank and repeat samples. Every 10th sample must be a standard, blank or repeat sample but the order of these can be varied and an accurate record of sample number and QC sample type and code where appropriate must be maintained by the project leader.
- All polyweave bags are to be clearly marked on the outside with a black permanent marker and an aluminium tag with sample and bag numbers must be tightly secured at the top of each bag with wire, zip lock ties or twine.
Note: Once samples have been bagged they will be ready for dispatch and must not be reopened until they reach the laboratory. Collecting samples within the trenches is very important, It will allow to know the extent of Quartz veins, the variation of old mineralization inside the veins, and other structural features within the artisanal workings sites. For the Channel Sampling through a vein, ore bed, along a trench, etc.. the geologist will use a hammer and a chisel and in some cases a jackhammer to a channel of about 1 1 / 2 "to 4" wide by 1 "deep. The size of the sample can vary by difficulty of grooving (material hardness), but the width and depth will be constant. The sampler shall Clean the surface to be sampled and Extending the ground a very clean canvas to collect the fragments.