Rocks and Minerals

Basic Geology is required by the Investors and the thousands of people employed by the mining industry don’t need to know as much about the Earth as a geologist does. But they should know at least the basics of geology and have some knowledge of the more common rocks and minerals.

To the investor, who “puts his money in the ground”, a little knowledge can go a long way. For instance, an investor might some day benefit from knowing that low-temperature mineral deposits, such as most silver orebodies, change quickly with depth or that faulting can play havoc with an orebody.

Geology, the science of the earth, has many branches. We’ll deal here only with those that have direct bearing on finding mines, beginning with a discussion on how mineral deposits form in the Earth’s crust.

The five most abundant elements in the crust are oxygen, silicon, aluminum, iron and calcium. Elements bond together in chemical compounds to form solid crystalline substance known as minerals.

There are many thousands of different minerals, each with a definite chemical composition and crystalline structure. For instance, iron and sulphur combine in a definite ratio to form the yellowish mineral pyrite. Potassium, aluminum, silicon and oxygen combine in a definite ratio to produce the common rock-forming mineral orthoclase.

The common-rock forming minerals, like orthoclase, are almost all silicates – that is, minerals containing silicon and oxygen. Sulphides are minerals with elements chemically bonded to sulphur, whereas oxides have elements bonded with oxygen. The fourth most important mineral group is the carbonates, in which carbon and oxygen are bonded with other elements.

What is the difference between an rock and a mineral? A rock is simply a solid mass of mineral grains. A rock is classified according to the kinds and proportions of minerals it contains.

Where minerals are concentrated in sufficient quantity, the zones or bodies in which they are found are called mineral deposits. Mineralization becomes ore when minerals are present in sufficient quantity, or tonnage, and adequate quality, or grade, to be recovered profitably.