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How Do Gold Nuggets Form in a River?

Gold is a precious metal which is universally valuable. It has been used as a source of currency since ancient times, with the United States abandoning the gold standard only as recently as 1933. Gold fueled the famous California Gold Rush of the mid-19th century. During the rush, prospectors would often pan for gold in streams and rivers. These gold nuggets experienced a long process in order to get into the prospector's pan.

Gold formation
- Gold is a precious metal.
  
  Gold is an element typically found deep inside the Earth. When tectonic plates move and collide, new mountain ranges form and gold is brought closer to the surface. Gold can also be pushed to the surface as a component of lava in volcanic eruptions.
Erosion
- Over millions of years, the mountains which hold deposits of gold experience erosion. Erosion is the process by which material is moved by the forces of nature. Water, in the form of precipitation and rivers, gently washes the surfaces of mountains. Over time, this can create deep cuts into mountains and expose the underlying gold. Next, water erosion leads to tiny particles of gold being washed into the streams.
Beginning Nugget Formation
- Once particles of gold enter the water, chemical processes separate gold from various alloys into pure gold. This is caused by the acidity of the water, and also by the presence of sulfides common in spring water. A process known as "cold welding" occurs which naturally binds the smaller flecks of gold into larger pieces, eventually forming larger and larger pieces of gold. This happens when the pieces of gold collide with each other in the swirling waters.
Finishing of Nugget Formation
- The larger pieces of gold continue to add more gold particles, and the nuggets are polished by the sediment in the moving water. The heavy weight of the gold eventually allows the nuggets to settle in the bottoms of streams and rivers.

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