Deposits are geological structures in which a certain substance or group of substances is found in much higher concentration than normally. For example metal deposits where certain metals are concentrated are called ore bodies, the metal bearing compounds are called ores. The economically relevant substances are called resources.
Mineral resources, especially ores, are actually distributed throughout the earth's crust. Rocks are eroded by the atmosphere and atmospheric water, and substances are dissolved and redeposited elsewhere by groundwater, especially when it forms convection currents due to volcanic heat. Due to the fact that many processes are specific for one substance, it can come to the accumulation of this substance at one place. This is then called a deposit.
Deposits can be different, differing, for example, in the proportion of the substance mined. Thus, the use of a deposit depends on whether one has procedures to extract raw material and whether this is economical. Especially in the last two centuries, the processing industry has made great progress, which has fundamentally changed the mining of some substances. In the Middle Ages, only high-grade ores could be smelted, but labor was cheap, small deposits of high-grade ores were mined. Today we have machines and can process large quantities of poor ores, but labor is expensive.