Cooling Process Importance on Mineral Formation

The Earth has a solid core of iron and nickel surrounded by a mantle of molten rock. When this material forces itself into many cracks and other points of weakness in the crust, it is called magma. These tongues of molten rock, which move out in many directions, heat the surrounding rock, altering it and, in some cases, causing it to re-melt. The whole mass then cools and that is when minerals, some of which are valuable, begin to crystallize.

Mineral constituents of molten lava crystallize at different temperatures. As a result, they tend to concentrate during the cooling process. It is these concentrations that often form mineral deposits. As each different mineral crystallizes out of the magma, the composition of the magma changes. Heavier metals sink to the bottom of the semi-liquid mass and are concentrated in a process called magmatic segregation. Some magmas have no valuable minerals, while others contain economically exploitable mineral deposits. 

Other deposits maybe formed by the minerals dissolved in the circulating liquids in and around magmas; these are redeposited at some places where chemical and physical conditions permit. These processes are known as hydrothermal processes.

When hot, sulphide-laden fluids spew up through fractures in the sea floor, these fluids form layered volcanogenic deposits. These are an important source of zinc, copper and lead.

The processes of weathering can also produce economic concentration of minerals, for example, placer gold found in river beds.

Because no two orebodies are alike, comparison among mines is risky. Just because ore on a particular property continues to depth does not mean that ore on an adjoining property will follow the same trend.