Table 1.

The five source group classifications used.

Classification	Structure
Two-cluster	Each source sample is assigned into one of two clusters according to the results of a k-means cluster analysis.
Three-cluster	Each source sample is assigned into one of three clusters according to the results of a k-means cluster analysis.
Four-cluster	Each source sample is assigned into one of four clusters according to the results of a k-means cluster analysis.
Geology classification 1	The original four geology source groups are combined to produce as many new source groups as possible with the requirement of very strong discrimination between them.
Geology classification 2	The original four geology source groups are combined to produce as many new source groups as possible with the requirement of moderate discrimination between them.