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A soil sample ready to be sieved.
The sample is sieved on-site using a 80 mesh sieve, 178 micrometers, using a stack of sieves with
progressively finer mesh sizes. This ensures that the finer clay and silt size particles are concentrated
as this is the particle size range which contains the highest concentration of
common indicator elements such as copper, lead, zinc and arsenic.
Sieving also removes coarse quartz grains which may have coarse or nuggets
gold attached. At first, this may seem like an odd thing to do removing the coarse
gold from the sample. The reason why it is done is so that the resultant
geochemical data has a smooth gradient and doesn’t contain spikes in the data or
unusually high values which can be difficult to map and contour.
In contrast in areas where deep moist soils exist, a hand soil auger is usually used
to obtain soil samples. Hand augering down to a depth of a metre or more is
sometimes necessary to obtain a sample from the top of the weathered rock. Soil samples by this
method are almost always moist or wet, so sieving is not possible. Mud tends to stick to the sampling
equipment so a nylon brush is used to clean most of the dirt and mud off before the next sample is
collected. Otherwise, cross-contamination can occur. Wet samples are placed in plastic bags and
submitted to the laboratory as is. The laboratory then does the drying and sieving required prior to
analysis.
Which Sample Was That?
Sample numbering using a foolproof method is extremely important. Due to the large number of samples
taken during a soil survey, great confusion can occur if numbering is not systematic. One of the best
methods is to use a pre-numbered ticket book. At each site the coordinates are entered into the ticket
book, the number is written on the outside of the sample bag with a permanent marker and the duplicate
ticket is torn out of the book and placed in the bag with the soil.

Analysis of samples
Before samples are submitted to the laboratory the geologist determines the suite of elements to be
analyzed and what the detection limit should be. As labs charge more for lower detection limits, budgets
come into play with both the suite of elements analyzed and the methods used.

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