Primary and Secondary Deposits

Primary deposits are mined either by open-cast (open-pit) mines or underground mining.

Secondary mining is alluvial, coastal, or marine mining.

Secondary diamond deposits are concentrations of diamonds removed from primary deposits by natural processes at the Earth's surface. Secondary deposits can occur in the vicinity of the parent rock or any distance up to many hundreds of kilometers away. They can be found in ancient or modern river beds, beaches, or as sea-bed deposits.

Gravel is alluvial deposits of silt, sand, and gravel. They may not contain economic minerals such as diamonds.

Alluvial - made up of or found in the materials that are left by the water of rivers, floods, etc. Alluvium (from the Latin, alluvius, from alluere, "to wash against") is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel.

Diamond is also found in rivers and streams or rocks around extinct volcanoes. This is because the igneous rock that makes up the volcano gets worn away by wind and rain over the years. Pieces of the igneous rock and diamond are carried down by the wind or in streams and rivers and, over many years, can get stuck together with lots of other pieces of sand and clay to form sedimentary rocks.