Which sourcing method is primarily used before South Africa's dominance?

The correct answer highlights alluvial washing as the primary sourcing method used before South Africa's dominance in diamond production. Alluvial washing refers to the process of extracting diamonds from riverbeds or shorelines where they have been naturally deposited over time. In this method, miners typically search for diamonds in sediment that has been transported by water. During the early discovery of diamonds, particularly in places like India, this was the prevalent technique because diamonds were often found in alluvial deposits.

Before large-scale mining operations transformed the industry, alluvial washing was accessible to many prospectors, allowing for relatively straightforward diamond recovery without the need for extensive machinery or technology. As mining techniques advanced and large deposits were discovered in South Africa, particularly in Kimberley, the industry shifted toward mining methods that could extract diamonds from deeper underground sources.

This context helps clarify why alluvial washing was significant in earlier diamond sourcing methods before South Africa's emergence as a dominant player in the diamond market.