A case study on geochemical anomaly identification through principal components analysis supplementary projection

Based on a case study in which a single geochemical anomaly was located in the vicinity of an abandoned mine in Central Portugal, a recursive methodology for anomaly/background separation was developed. This methodology relies on the supplementary projection of each of the samples taken from a subset of ‘anomaly candidates’ onto the axes provided by Principal Components Analysis of the background subset. The concept of ‘anomaly intensity’, defined by the average of the distances from the original to the supplementary projections, is the basis for final anomaly identification.