Prospector's gold scales. Miners carried these small scales when prospecting. Prospecting for placer gold is normally done with a gold pan or similar instrument to wash free gold particles from loose surface sediment. The use of gold pans is centuries old, but is still common among prospectors and miners with little financial backing. Deeper placer deposits may be sampled by trenching or drilling. Geophysical methods such as seismic, gravity or magnetics may be used to locate buried river channels that are likely locations for placer gold. Sampling and assaying a placer gold deposit to determine its economic viability is subject to many pitfalls. Once placer gold is discovered, the gold pan is usually replaced by sluices or mechanical devices to wash greater volumes of material. Discovery of placer gold has often resulted in discovery of hardrock gold deposits when the placers are traced to their sources.