Final answer:
Placer deposits concentrate ore minerals primarily through mechanical separation methods like panning which uses the physical properties of minerals to differentiate them. Techniques have evolved from simple panning to complex scientific methods, including chemical processes like hydrometallurgy for metals like silver and copper.
Step-by-step explanation:
Placer deposits concentrate ore minerals primarily by mechanical separation from their host rock or sediment. This process relies on the physical properties of the minerals, such as density and resistance to weathering. In the context of gold mining, for example, prospectors historically used panning, in which lighter sediment is washed away, leaving the denser gold nuggets or particles behind. Modern hydraulic mining and other scientific methods have since replaced these older techniques for large-scale operations. During the California Gold Rush, methods like panning or using rockers and sluices were commonly employed to separate gold from placer deposits. Additionally, the use of mercury was introduced to recover fine gold, forming an amalgam that makes collection easier.
Preliminary treatment in ore processing can involve crushing or grinding to liberate valuable metals, followed by concentration of the metal-bearing components. In some cases, further chemical treatment is used to produce compounds that can be more easily reduced to the metal. This can be seen in the isolation of metals like copper and silver, where methods like hydrometallurgy can be used to selectively dissolve and recover the target metal from its ore.