Fig. 3

Principal component analysis overview A PC1 versus PC2 scores plot shows clear differentiation between specimens collected by Grant, Grant with Cairn, from those collected by Broadbent. B The variable loadings plot shows the elements Zn and Pb describe Broadbent’s specimens long PC2, while a high relative concentration of As describes specimens collected by Grant with Cairn along PC1. C The X-Explained Variance plot shows that two PCs explain over 97% of the XRF data for both calibration and cross-validation sets