placer deposit

Their name derived from the Spanish term for a sand bank, placer deposits contain gravel or rocks rich in a valuable mineral—usually gold, platinum, diamonds, or tin. These materials have been washed out of ore veins, carried, and laid down as alluvial deposits at places in a river where the current slows, such as below a rapids. Placer deposits—the word rhymes with “sass her” not “place her”—are usually the first to be mined after a strike. They’re at or near the surface, and the running water that laid the deposits down initially is often close at hand, a ready source for hydraulically sorting this (already) loosened material. It’s placer mining that gave rise to the enduring image of a lone prospector panning for gold along a western stream.

Barbara Kingsolver