What are RC drilling error sources and mitigation strategies?

Contamination can occur when insufficient air is returning up in the inner tube

Worn inner tubes. Excess air escaping up the drill hole annulus

Weighing and documentation of sample size. Regular inspection of the inner tubes

Contamination by a material scraped from the wall

Raising or lowering rods in a hole can cause scraping material from the wall which falls to the bottom of the hole. Holes in soft ground and also inclined holes are particularly prone to this type of contamination

The material on the bottom of the hole should be discarded and sampling recommenced only after fresh rock is exposed. This precaution should be always taken when a new rod is added to the drill string

Use of blow back device to clear the inner tube also causes scraping material from the wall

Contamination in the inner tube

When drilling sticky clay-rich formations the clay can build up in the inner tube obstructing the normal air flow and causing contamination of the samples

Weighing and documentation of sample size with particular attention if samples are wet; Regular inspection of the inner tubes

Contamination in the cyclone

Cyclones can selectively trap the rock cuttings because of the mechanical damages of the cyclone surfaces or their suboptimal design

Cyclones should be regularly checked, in particular after changing between wet and dry grounds. Do not hit the body of a cyclone to remove stuck sample

Contamination because of poor cleaning cyclones after wet sticky samples

Check the internal surface and clean it regularly

Splitter generates non-representative and/or biased samples

Incorrectly designed or mechanically damaged splitter can cause disproportional splitting of the different material types and/or losses of the fines

Regularly check and clean splitters; Duplicate samples should be regularly collected from splitter and assayed to monitor the sample repeatability (Abzalov 2008)