Low density geochemical mapping and mineral exploration: application of the mineral system concept

The mineral exploration industry is used to very high sample densities (100s to 1000s of samples/km(2)) for geochemical exploration in order to define drill targets. Lately, geoscience organizations in many countries have been geochemically mapping increasingly larger areas at progressively lower sampling densities (1 site/100 to 1 site/18 000 km(2)). A single ore body is too small a target and cannot be expected to be discovered at such low sample densities; indeed numerous deposits could be hidden within a 100 x 100 km grid cell. However, mineral systems, which include all geological ingredients and processes necessary for the generation of mineral deposits, form much larger targets that could be identified even at such low sampling densities. Examples from some European low density geochemical surveys where patterns emerged that may have implications for mineral exploration are shown and discussed. It is concluded that low density geochemical mapping holds great promise in the early stages of mineral exploration programmes in guiding subsequent effort into the more fertile regions. Interpretation of these maps, however, may need a different approach than that used in classical, high density mapping exercises, where only 'high values' of certain metals are the traditional target.