Coastal placers are rich in many important building materials and metals, such as diamond, cassiterite, gold and so on. The minerals in the rocks in the coastal zone are constantly weathered, and some mineral particles are transported to the beach after being washed by rain and rivers.
After entering the ocean, mineral particles are further screened and sorted under the action of ocean power such as waves and currents, and minerals with similar specific gravity accumulate together to form ore belts. After the placer deposits on the seashore, when the sea level drops, the coastal placer will be exposed to the sea surface. When the sea level rises, the coastal placer will be buried on the seabed and become an ancient coastal placer. This is why placers form on the seashore.