Gold-quartz placer nugget (derived from auriferous Precambrian basement rocks; Elk Creek, west of Rt. 285 & southeast of Lead, Black Hills, South Dakota, USA) 1
Gold-quartz placer nugget from the Black Hills of South Dakota, USA. (1 centimeter across at its widest)
This is a modern fluvial pebble composed of native gold (Au) and quartz (SiO2). The gold is ultimately derived from auriferous Precambrian basement rocks in the area of Lead, South Dakota. The now-inactive Homestake Mine, America's largest gold mine, is located in Lead (pronounced "Leed").
Gold masses that accumulate in river or stream gravels, or get trapped in fractures in bedrock-floored rivers, are called placer deposits - such gold is called placer gold.
Locality: attributed to Elk Creek, west of Rt. 385, southeast of the town of Lead, northern Black Hills, western South Dakota, USA.
Photo gallery of gold: