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Typical layout of a soil sampling programme. Base image: Google Earth.

Taking Soil Samples
Soil sampling is a lot easier now that a GPS is standard equipment, so the uncertainly of where the actual
sample comes from is minimized. The team uses the coordinates that were entered into the GPS to locate
each site. Normally, this can be done to an accuracy of ± 5m, which is the typical accuracy of a hand-held
GPS.
Soil Sample with Friends
Soil sampling is normally done with a minimum of two people; a geologist and a field assistant. This is
not only for getting the work done more quickly, but for safety reasons too. As with any work in remote
areas emergencies can happen when least expected, which can lead to life threatening situations. Once
while soil sampling, my assistant had an asthma attack triggered by fungal spores in a particular soil
sample. The fungus had apparently grown on sheep dung. Fortunately, her medication wasn’t too far
away in the truck and she recovered quickly. The moral of the story here is to be prepared at all times.
No Jewellery Please, We’re Soil Sampling!
All Jewellery such as rings, bracelets and necklaces must be removed by those directly involved in
collecting and handling the samples. This eliminates any chance of jewellery coming into contact with a
sample and contaminating it. Gold and silver are obviously a risk, but I once knew a company that got
excited by a “palladium anomaly” which was later found out to be caused by the sampler wearing a
platinum ring. Both platinum and palladium commonly exist together as they both belong to a group
known as the platinum group metals (PGM).
Another source of contamination can come for the sampling equipment itself, such as lead-silver solder
used to attach the mesh to the outer ring in some sieves and chromium from stainless steel picks and
shovels. Even the type of sunscreen used by the samplers must be considered, as zinc based creams can
contaminate samples from sweat off the skin.

Local Site Contamination
Sometimes, the actual location of the sample site can cause problems too. Some wood preservatives
used in fence posts can contaminate the soil and hence nearby samples with chromium and arsenic.
Corrugated galvanized iron in close proximity to sample sites can result in elevated zinc levels. The
possibilities for contamination are numerous, so one must always be on the lookout for potential
sources.
Start At The Most Interesting Line
The first line that is sampled is usually the one with the highest probability of encountering a soil
anomaly. The reason for doing the “best” lines first is so that if the sampling cannot be completed for any
reason, e.g. bad weather or a twisted ankle, then it is not so much of a great loss.

XRF Spectrometry
Another way of saving time and money on a sampling programme is to use a hand-held X-ray
fluorescence (XRF) spectrometer on each sample as they are being collected. This quickly gives the
geologist an idea as to whether or not a geochemical anomaly is being detected during the programme.
By using the instrument in the field, the sampling programme can be modified as it proceeds. Soil lines
can be dropped while others can be added to infill the survey. If a geochemical anomaly is suspected the
spacing between sites can be done reduced, say from 20m to 10m.

How to Take A Soil Sample
In country where the soil cover is quite thin, a sample is obtained by digging a small hole with a long
handled pick, usually down to weathered rock. The sample is then placed into the top sieve with a small
garden spade. This coarsest sieve removes organic matter such as leaf litter and charcoal as well as
coarse sand and gravel.

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