Chapter 12: Riches in Rock: Energy and Mineral Resources
Study Plan
The Homestake Gold Mine in South Dakota occurs in Precambrian rocks of the Black Hills. Pegmatite dikes formed when steamy magmas injected into cracks in older metamorphic rock. Gold carried by the magmas and hydrothermal fluids crystallized in small flakes dispersed through the rock. This is an open-pit mine, representing the result of years of excavation by massive equipment.
Credit: Stephen Marshak
Guide to Reading
Rocks and minerals are the natural energy resources that provide the essentials of modern life and industrial society: electricity, fuel, and a range of raw materials for manufacturing products. This chapter presents an overview of the many resources. Since you've had all these chapters' worth of geology background, it's assumed you already know the basic rock types, geologic structures, geologic time, and Earth history. Therefore, while this chapter doesn't need to introduce many new concepts, there are many new terms to become familiar with.
Your author begins with basic sources of energy on Earth and then goes into detail about the energy resources modern society relies on most, fossil fuels (petroleum, natural gas, and coal). To understand the diverse makeup of petroleum (oil), you learn the basic organic chemistry of hydrocarbons.
How do oil and gas form and accumulate? You read about plankton; source rock and reservoir rock; porosity and permeability; oil reserves, traps, and seals.
How do you find petroleum, get it out of the ground, and process it? Constantly rising prices make this a hot topic. When (not if) the world runs out of commercial quantities of oil, what are some possible hydrocarbon alternatives? Your author discusses tar sands (oil sands), oil shale, natural gas, and gas hydrate.
Coal is another fossil fuel and the next-most-used energy resource. You read of its formation from swamp plant material and its sequence of development. How much does the world depend on coal for energy, can this situation change, and how wise is it to become more dependent on yet another fossil fuel?
A few decades ago, when the world started to become concerned about the future availability of fossil fuels, nuclear power seemed to many people to be the answer. Why hasn't it become the world's chief energy source? You start by learning about the chain reaction that generates energy. Just how dangerous is nuclear energy? You read about the risk of meltdown and consider that the use of nuclear power has become a touchy societal issue. One of the chief concerns is, "What do we do with the nuclear wastes?"
The next part of the chapter is based on an opinion held by most experts in both science and industry: We have been living in a unique and very limited time in human history, the Oil Age. From the human viewpoint oil, gas, and coal are nonrenewable resources. Your author introduces geothermal energy, hydroelectric power, solar power, wind power, ethanol, and fuel cells.
There seems to be no perfect answer; each energy option has advantages and disadvantages in terms of efficiency, cost, political consequences, and environmental impact. But it does seem as though some choices must be made and some steps taken soon so that the Arabian saying doesn't become reality: "My father rode a camel. I drive a car. My son rides in a jet airplane. His son will ride a camel."
The next part of this resource chapter introduces many of the mineral resources that give us the raw materials for our very comfortable lifestyles in our industrial society. It discusses the geologic reasons for their existence, methods of extracting them from the Earth, products made from them, concerns about future supplies, and the environmental impact caused by their extraction.
The raw materials are both metallic and nonmetallic. Metals are generally less abundant and more expensive than nonmetals, and some are not only useful to humankind but are highly prized by society. The native metal, gold, influenced the course of history in our own West and worldwide. The author discusses ores - rocks or minerals that contain metal in high concentration. Topics of discussion include:
- How can you classify ore deposits? On the basis of their origins: magmatic (including massive-sulfide deposits), hydrothermal (including disseminated and vein deposits, and black smokers), secondary-enrichment deposits (including copper carbonates like azurite and malachite), sedimentary deposits (including banded-iron formations and manganese nodules), residual mineral deposits (like bauxite, that are left after leaching by groundwater), and placer deposits (of dense materials).
- Where do you look for ore deposits? Metallic minerals aren't evenly distributed worldwide. Why are deposits found in some places and not in others? Plate tectonics, of course! You get details of ores in the Andes of Peru and in the western United States. You've gotten so used to plate tectonics being the reason for everything, you may be surprised to learn plate tectonics had no direct bearing on the formation of banded-iron formations (BIFs) or on residual ore deposits like bauxite.
In all those discussion of metals, and throughout the rest of the chapter, the author has had to make choices of what examples he'll use. While it's never a bad idea to learn as much detail as is reasonable, it's most important you understand the concepts being explained by use of the examples. Your teacher may use local examples of minerals to illustrate concepts.
Nonmetallic mineral resources don't have the glamour of gold, but they're very useful to humankind. Centuries ago people began to quarry stone to construct impressive and enduring buildings, and as time has passed, society has continued to use building stone and numerous other nonmetallic resources. The chapter mentions many of these resources and products made from them, including cement, concrete, gravestones, flagstones, bricks, crushed rock, window glass, asbestos, landscaping rock, salt, and gypsum.
Not only has society become very concerned about the diminishing amounts of energy reserves; it is also starting to be concerned about diminishing amounts of mineral reserves. As with energy resources, mineral resources are nonrenewable and unevenly distributed around the world. This causes economics and politics to play important roles in any scenario that concerns mineral reserves. How long a resource lasts depends in part on how badly people want it and what they're willing to pay for it. Many of these materials have caused conflict in the past; the United States stockpiles some of its strategic metals in the hope of avoiding some battles in the future.
The chapter ends with the sensitive topic of mining and the environment. Extracting minerals on a large scale can be costly to the environmental quality on Earth. Balancing our material desires with minimal environmental impact is becoming a growing challenge.
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