Occurrence

Sapphires are contained in ancient deposits of 'wash'. The bottom in many places is granite, and slate in others, although at the Willows Field the bottom is generally clay overlaying sandstone. The wash varies in depth from the surface to 60 feet or more, but over large areas the wash is from one to three feet in depth. Gutters in the bedrock appear to influence the deposits of sapphires. The sapphires are not found in the beds of the gutter unless the beds are very tough. Rather, they are found in the banks. Consequently, it is general practice, when working a gutter, to work up towards the higher ground. Not all wash is gem-rich, but 'billy' boulders are always present where sapphires are found, so the occurrence of 'billy' is considered not only favourable, but also essential.

'Billy' is the term given to a very hard, dense siliceous rock of characteristic boulder appearance. Basalt boulders in a decomposed state are sometimes found in the wash and are considered a very favourable indication. Sapphires are associated with many other minerals such as plain corundum, amethyst, zircon and garnet, and the presence of these minerals in the wash is a favourable indication.