2.2.4 Geochemical Surveys

Geochemical surveys are used to detect chemical anomalies, that is, abnormally high concentrations of chemical elements.

A deposit is a geochemical anomaly. It often forms as a result of a specific geological event which leads to the concentration of unusual minerals, rich in valuable chemical elements.

If a deposit at or near the surface is exposed to the forces of water, wind, snow and sun, its chemical elements are dispersed in nature.

Traces may then be found in the soil, underground and surface water (lakes, rivers), vegetation or even in the air.

A geochemical survey involves taking samples of soil, sediment from rivers and lakes, surface and underground water, vegetation or air and then having them analysed in a laboratory.

		Precious metals may be found in vegetation. So it is a good idea to take samples of the flora.
	Source

The contents of chemical elements, usually expressed in parts per million (or ppm), are then recorded on a map, in order to detect any chemically anomalous rocks.

Geochemical surveys are often used as a reconnaissance method to identify areas that might have mining potential.

		Geochemical map showing the nickel content in the Chapais region (Québec).
	Source