A background to the use of empirical indices (i.e. ratios and sums) in exploration geochemistry is presented, together with commentary on more sophisticated statistical multivariate procedures. Multivariate statistical procedures can assist in developing geochemical models upon which further investigations can be based, and in identifying geochemically anomalous samples. A case is made for a simple method, weighted sums, that is based on prior knowledge concerning the mineralogy and geochemistry of sought-after mineral resources. This procedure avoids many of the complications and pit-falls of more sophisticated multivariate statistical methods. Although weighted sums were introduced to exploration geochemistry over 20 years ago, they don’t appear to have been used extensively. The objective of this paper is to reintroduce them, with a simple but clear exposition, as a tool worthy of consideration in the knowledge-based 21st century.