Low-density geochemical mapping and the robustness of geochemical patterns

Abstract

Geochemical mapping of entire continents and, ultimately, the world is still a challenge for applied geochemists. At sample densities traditionally used for geochemical exploration (1 site per 1–25 km 2 ), geochemical mapping of whole continents is logistically extremely demanding and tremendously expensive. The first low-density geochemical surveys (1 site per 200 km 2 ) were carried out during the late 1960s in Africa. Later surveys conducted in various parts of the world had sample densities ranging from 1 site per 300 km 2 to 1 site per 18 000 km 2 . Although these surveys were deemed successful by the investigators in defining variations in background element content on a regional scale, the scientific community was sceptical that low-density geochemical mapping was possible and would provide useful information. The main area of criticism centred around the concern that at such low sample densities the resulting maps would not be robust, i.e. if the same area were resampled and remapped, different geochemical patterns would emerge. Different examples from the USA, Europe, China and Africa demonstrate that low-density geochemical mapping will result in stable and robust geochemical patterns at the continental scale. Such maps are urgently needed for a wide variety of applications.