Perhaps the most notable thing about skim placers is that they form on the top surface of gravel bars, as opposed to coarser gold placers where the weight of the gold particles allows the gold to settle down on or near bedrock.

The type of mine dump that is best for metal detecting are the ones that consist of mixed sizes of rock and are located near some sort of excavation, commonly a shaft or adit. Sometimes the piles located along a trench dug by the miners can be productive as well.

With successively lower temperatures as the water mixture cools, new sets of minerals are formed and many of those stable at a higher degree of heat became subject to alteration as the temperature progressively moved lower.