Chapter 15

What are some environmental hazards of large-scale mining?

The costs of mining can be immense. To get a rough sense of this expense, imagine that an ore deposit of a certain metal contains $$0.6\mathrm{\%}$$ grade ore. This means that $0.6\mathrm{\%}$ by weight of a block of ore consists of the metal. On the open market, the pure metal sells for $$\mathrm{\$}8,000/$$ ton. It costs $$\mathrm{\$}15/$$ ton to mine the ore, $$\mathrm{\$}15/$$ ton to transport the ore to the processing plant, and $$\mathrm{\$}15/$$ ton to process the ore and produce pure metal. Start-up costs (building the mine and building the processing factory) are about $$\mathrm{\$}100$$ million. How much profit does the company make when it sells a ton of metal? How much ore (in tons) does the operation have to mine to pay back the start-up costs? Considering that a giant dump truck in a mine can carry 200 tons of ore at a time, how many dump-truck loads will have been transported at the break-even point? If the mine has eight trucks that can each make six loads a day, about how many years will it take to break even?

An ore deposit at a location in Arizona has the following characteristics: One portion of the ore deposit is an intrusive igneous rock in which tiny grains of copper sulfide minerals are dispersed among the other minerals of the rock. Another nearby portion of the ore deposit consists of limestone in which malachite fills cavities and pores in the rock. What types of ores are these? Describe the geologic history that led to the formation of these deposits.