Putting Down A Deposit
© AMNH Exhibitions
In nature, gold deposits occur as veins or as placers.
Most crystalline gold comes from hydrothermal fluid, extremely hot water rising from deep in the Earth. As the fluid moves through openings in Earth's rocky crust, tiny amounts of gold dissolve into it. Then, as the fluid flows through cooler rocks near the surface, the gold precipitates, or is drawn out of the fluid, and settles in cracks to form veins or lodes.
Over millions of years, gold flakes and grains worn away from veins are swept into bodies of water. The heavy gold settles in stream-, lake- and riverbeds, and on the sea floor, forming placer deposits.
© AMNH / Craig Chesek Gold and quartz vein in metamorphic rock, San Antonio Mine, Manitoba, Canada. On loan from the Royal Ontario Museum.
Microscopic particles of gold can be extracted from rocks. After gold-bearing rocks are pulverized, the gold is recovered using chemical processes. Nearly 40 percent of all gold ever mined was recovered from rocks from South Africa.
Gold nuggets are solid lumps of gold. The term "nugget" was first used for gold in 1852 during Australia's gold rush.
Nuggets are often named for their appearance. The variety of names reflects the many possible shapes of native gold.
The rounded surfaces of many of these nuggets show that they were worn smooth in streams or rivers and collected from placer deposits.
Nuggets are rare, making up less than 2 percent of all native gold ever mined.