Mineral Resources

Mineral Resources Definition

Combine the two definitions together, and we have a mineral resource.

Minerals have a defined chemical composition, for example gypsum is also known as calcium sulfate dihydrate, or CaSO₄·2H₂O. Minerals are also categorized based on their unique physical properties, such as:

• Colour
• Density
• Lustre
• Streak
• Cleavage
• Hardness.

While the definition is straightforward, it doesn't exactly fit for all mineral resources.

• Most glaringly, oil is clearly categorized as a mineral resource, yet it is a liquid, and it comes from organic sources (decaying and buried organic matter).
• Limestone is also formed from organic sources (e.g. corals, bivalves, molluscs), and this arguably makes it renewable as well.
• Granite, for example, is essentially renewable, since new plutons are being formed below the Earth's crust every day.

Yet, at over millions of years to form new limestone or granite, the rate of renewal often outdates us so drastically that it cannot be truly considered renewable.

Mineral Resources Types

Mineral resources are classified into distinct categories (Fig 1.). The first two major types of mineral resources, metallic and non-metallic, are based on the metal content of the mineral resource.

Metallic mineral resources are further split into two groups, ferrous and non-ferrous, based on whether the metal contains iron.

Every so often, you may come across a separate category for a special subset of non-metallic mineral resources: fuel. As previously mentioned, fuels are generally pretty unique. Not only are they easily combustible, but they also barely fit our definition of mineral resource. They can be found in solid (coal), liquid (petroleum), or gaseous (natural gas) phases. Fuels are not inorganic, they are the product of decayed organic matter. Largely, fuels are non-renewable and naturally occurring, but this part of the definition is also tenuous. As we speak, engineers are hard at work trying to develop a method to extract natural gas from animal wastes. Nonetheless, fuels are still a mineral resource.

Sources of Mineral Resources

The source of almost all mineral reserves is the lithosphere, which is the upper part of the Earth's crust. As you will learn, there are three different geological sources that form mineral resources. The common link between these sources is that they transport and accumulate minerals.

Magmatic Sources

Most mineral reserves are a direct result of magmatic bodies.

Eventually, a magma chamber stops being replenished with magma, and starts to cool down. During the slow cooldown phase, minerals form preferentially within the magma chamber, a process called crystal fractionation. Magma is the most common source of rare earth elements. Other minerals derived from magma are feldspar or mica minerals. Perhaps you own a granite countertop that was once a buried magma chamber.

Fig. 2. An illustration of two possible mechanisms, a) or b), of mineral formation in magma chambers. The steps c, d and e are similar for both processes.

Sedimentary Sources

There are numerous types of water bodies, and each yields their own unique mineral resources. Generally speaking, most water bodies will accumulate minerals as some form of sedimentary deposition. A small, quiet, inland lake, after being separated from a river, allows fine clay particles to settle, creating a clay mineral deposit. Evaporating saline lakes leave behind salt flats. These special minerals, evaporites (Fig. 3), can be harvested for gypsum, lithium, or table salt.

Bogs are distinctly renowned for generating peat, which is the first step to coal formation. High velocity water bodies, such as rivers and streams, leave behind placer deposits. The river drops heavier materials, like gravel, or heavy metals such as gold, while carrying away all other finer materials such as sand, silt, and clay.

Fig. 3. A picture of the Uyuni salt flats in Bolivia. The evaporites at this location are a mix of sodium, potassium, lithium, and magnesium chlorides.

Hydrothermal Sources

Some minerals are created when water (hydro-) percolates downwards through the lithosphere, and reaches a heat source (-thermal). The water heats up, and is capable of dissolving more solute. The water eventually flows away from the heat source, carrying along dissolved chemicals. As the water cools down, the minerals precipitate out of solution, creating hydrothermal deposits. Here are three major hydrothermal sources for mineral reserves.

Sulphide Deposits

Sulphide deposits are a specific type of hydrothermal source (Fig. 4) found at tectonic plate spreading centres at the bottom of the ocean. Metal and sulphides are dissolved in ocean water near these hot spots. The dissolved minerals later precipitate out of solution when the solute reaches cooler ocean water.

Fig. 4. A hydrothermal vent in the Mariana Trench. Notice the yellowish brown features on this vent, which is indicative of sulphide minerals. NOAA Ocean Exploration.

Vein Deposits

Vein deposits are mineral reserves precipitated out of solution in the bedrock cracks around a magma chamber. These result in quartz and calcite veins, but also yield precious metals such as gold, silver, and copper. Occasionally, these mineral reserves can contain rare earth minerals.

Stratabound Deposits

Stratabound deposits are mineral reserves accumulated in a sedimentary rock layer, or strata. Sedimentary rock layers tend to have a high percentage of void space per volume, known as porosity. When thermally heated water flows through these rock layers, it may precipitate out minerals. Examples of stratabound deposits are the minerals containing lead, zinc, or copper metals.

Examples of Mineral Resources

Now that you have learned how to classify mineral resources, let's review some examples of minerals we humans are actively mining. The following table has sorted the examples of mineral resources by type in the vertical columns, and by source in the horizontal columns.

Table 1: Examples of mineral resources by type and source.

Importance of Mineral Resources

Now it is time to learn the importance of mineral resources and the impact these minerals have on our lives. Most importantly, and perhaps obviously, the mining of mineral resources supplies the raw materials we use to build the objects surrounding us. Combined with the use of technology, humankind has the uncanny ability to turn a shapeless lump into an object with an application. From the first wheels constructed out of stone during the Palaeolithic, all the way to nanocomputers and satellites, the importance of minerals as building blocks should be self-evident.

• Clay is used for pottery, bricks, and tiles.
• Metals are critical in the domains of industry, and transportation, and electronics.
• Gypsum is used to make plasterboard.
• Sand, soda ash and limestone are combined to manufacture glass.
• Plastics are derived from fossil fuels.

The list is endless.

Furthermore, we have been able to extract energy out of mineral resources.

Economically, mining these resources is important. The location of mineral reserves is geologically defined, and therefore not equitably distributed within geopolitical lines. There, harvesting these minerals has created its own mining economy where trading minerals between countries is crucial. Below is a map of England, showing the location of a few active mineral mining operations (Fig. 5).

Fig. 5 A map of England, showcasing the mining sites for some mineral resources.

Hopefully, you now know more about mineral resources. Next time you treat yourself to a portion of chips, think about the mineral resource that the saltiness came from.