Gold is one of the most precious metals and is called a "noble metal" because it does not react with air under ordinary conditions. Gold is deposited from solutions containing dissolved gold.

There are two main types of gold deposits. When gold is found at the place where it was formed, the deposit is called a primary deposit, or a . When gold moves away from its primary location by wind, water, ice, or gravity, it can concentrate in another place to form a secondary deposit called a . In a placer deposit gold can be found as clumps (nuggets), as small particles, or as gold dust.

Gold is very heavy, and usually does not travel very far from its source. Miners often find placer gold in streams and pan their way up the stream until they reach the lode deposit. Much of the gold produced in Alaska was mined from placers.