Soil sampling is when the fine fraction of a soil or sediment is collected at discrete points, usually i a grid pattern, over a scale of several hundred metres.
It is a relatively quick and cheap method of identifying if gold exists at higher levels that is usual, which can then help focus more detailed and accurate sampling methods such as trenching and drilling.
The area selected for soil sampling will be based on a feature thought to be prospective for gold, usually a rock type, fault, geophysical response, or proximity to known gold mineralization, or a combination of all of these.
‘Soil’ in gold exploration terms means the loose material at the surface of a landscape, which is not the same as typical garden ‘soil’. Depending on the terrain, the black organic rich layer of soil is removed and the more rocky or silty material below sampled because this is a better representation of the rock beneath, which is where the gold deposit proper potentially occurs. Dilution usually occurs in soils/sediment because any sediment will have been transported and mixed to some degree with material sourced from adjacent areas. In the case of gold deposits, a mineralized area will have soil over it originating from the deposit but also adjacent barren areas.
Gold mineralization that is ‘blind’, meaning that it is underground and has no exposure to the surface, will not be identified by soil sampling.