The rocks of Earth’s crust and oceans are the source of a wide variety of useful and valuable materials. From the first use of rocks, such as flint and obsidian, to make tools during the Stone Age, the use of Earth materials has expanded, resulting in more complex societies and our modern civilization. The mineral and energy resources we extract from Earth’s crust are the raw materials from which we make all the products we use.

Natural resources are typically grouped into broad categories according to (1) their ability to be regenerated (renewable or nonrenewable) or (2) their origin or type. Here we will consider mineral resources. However, other natural resources are indispensable to humans, including air, water, and solar energy.

Renewable Versus Nonrenewable Resources

Resources classified as renewable can be replenished over relatively short time spans. Common examples are corn used for food and for making fuel ethanol, natural fibers such as cotton for clothing, and forest products for lumber and paper. Energy from flowing water, wind, and the Sun are also considered renewable ▼.

By contrast, many other basic resources are classified as nonrenewable. Important metals such as iron, aluminum, and copper fall into this category, as do our most widely used fuels: petroleum, natural gas, and coal. Although these and other resources form continuously, the processes that create them are so slow that significant deposits take millions of years to accumulate. Thus, for all practical purposes, Earth contains fixed quantities of these substances. The present supplies will be depleted as they are mined or pumped from the ground. Although some nonrenewable resources, such as the aluminum we use for containers, can be recycled, others, such as the oil burned for fuel, cannot.

Mineral Resources and Ore Deposits

Today, practically every manufactured product contains materials obtained from minerals. Mineral resources are occurrences of useful minerals that are formed in such quantities that eventual extraction is reasonably certain. Mineral resources include deposits of metallic minerals that can be presently extracted profitably, as well as known deposits that are not yet economically or technologically recoverable. Materials used for such purposes as building stone, road aggregate, abrasives, ceramics, and fertilizers are not usually called mineral resources; rather, they are classified as industrial rocks and minerals.

An ore deposit is a naturally occurring material with a concentration of one or more metallic minerals that can be extracted economically. In common usage, the term ore is also applied to some nonmetallic minerals, such as fluorite and sulfur. Recall that more than 98 percent of Earth’s crust is composed of only eight elements, and except for oxygen and silicon, all other elements make up a relatively small fraction of common crustal rocks ▼. Indeed, the natural concentrations of many elements are exceedingly small. A deposit containing the average concentration of an element, such as gold, has no economic value because the cost of extracting it greatly exceeds the value of the gold that could be recovered.

In order to have economic value, an ore deposit must be highly concentrated. For example, copper makes up about 0.0068 percent of the crust. For a deposit to be considered a copper ore, it must contain a concentration of copper that is about 100 times this amount, or about 0.68 percent. Aluminum, on the other hand, represents about 8.1 percent of the crust and can be extracted profitably when it is found in concentrations 3 or 4 times that amount.

It is important to understand that due to economic or technological changes, a deposit may either become profitable to extract or lose its profitability. If the demand for a metal increases and its value rises sufficiently, the status of a previously unprofitable deposit can be upgraded from a mineral to an ore. Technological advances that allow a resource to be extracted more efficiently and, thus, more profitably than before may also trigger a change of status.

Conversely, changing economic factors can turn what was once a profitable ore deposit into an unprofitable mineral deposit. This situation was illustrated at the copper mining operation located at Bingham Canyon, Utah, one of the largest open-pit mines on Earth ▼. Mining was halted there in 1985 because outmoded equipment had driven the cost of extracting the copper beyond the current selling price. In 1989, new owners responded by replacing an antiquated 1000-car railroad with modern conveyor belts and large dump trucks for efficiently transporting the ore and waste. The new equipment reduced extraction costs by nearly 30 percent, ultimately returning the copper mine operation to profitability. Today the Bingham Canyon mine produces nearly 25 percent of the refined copper in the United States. In addition to producing about 160,000 metric tons of copper, the Bingham Canyon mine produces about 7600 ounces of gold,  million ounces of silver, and  metric tons of molybdenum as well as a number of critical minerals.

Over the years, geologists have been keenly interested in learning how natural processes produce localized concentrations of essential minerals. One well-established fact is that occurrences of valuable mineral resources are closely related to the rock cycle. That is, the mechanisms that generate igneous, sedimentary, and metamorphic rocks, including the processes of weathering and erosion, play a major role in producing concentrated accumulations of useful elements. As these rock-forming processes are examined in the following chapters, we consider their role in producing some of our important mineral resources.

• Resources are classified as renewable when they can be replenished over short time spans and nonrenewable when they can’t.

• Ore deposits are naturally occurring concentrations of one or more metallic minerals that can be extracted economically using current technology. A mineral resource can be upgraded to an ore deposit if the price of the commodity increases sufficiently or if the cost of extraction decreases. The reverse can also happen.

• mineral resources: All discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future.

• nonrenewable: With respect to a resource, any resource that forms or accumulates over such long time spans that it must be considered as fixed in total quantity.

• ore deposit: A naturally occurring concentration of one or more metallic minerals that can be extracted economically. Ore can also refer to concentrations of important nonmetallic minerals.

• renewable: With respect to a resource, a resource that is virtually inexhaustible or that can be replenished over relatively short time spans.