Very often the copper you use doesn't always stand out to the casual observer. Likewise, a casual glimpse of Arizona's landscape could never have revealed the rich ore that lies beneath the surface. Other important minerals — like gold, silver, lead, zinc and molybdenum — are by-products of copper production, while copper combines with other metals to make beautiful bronze and brass. In the same way, Arizona's copper mining industry has made possible many other important businesses — from electric generation and production to life-saving medical technology.

From Prospect to Production
One of man's most basic industries, copper mining is also among the most important and ever-changing. Throughout its history, the mining industry has created wealth by locating, extracting and refining minerals for consumption by society. Previously, we described some of the many uses of copper. Now, let's look at how seemingly common rocks are transformed into usable products.

Copper had a fiery beginning, long before man or animal walked the earth. While it was copper that gave birth to the electrical age, volcanoes gave birth to copper. The volcanic age left copper deposits, hidden deep beneath the earth's surface, in a diagonal line from one end of Arizona to the other. Many centuries later, man would begin the almost magical process of mining.

Prospectors had First Pick
The early miners, in the 1800s, had it relatively easy. With pick and shovel, these old timers traveled on burros searching for deposits of relatively rich ore. Whether gold, silver or copper, important finds could be made simply by looking for signs of color in the rock. Reports exist of early miners in the areas of Ajo and Gila Bend hand-sorting colorful copper ore and shipping it by ox team across the desert to California, where it was loaded on flat boats and sent across the sea to Wales for smelting.

Those colorful mineral occurrences have long since disappeared. Soon after the mining industry took off in the 1800s, miners found that they could no longer mine rich copper deposits at or near the surface of the ground. Underground mines, and later open-pit mines, became the norm for extracting copper from the earth.

The first ore mined by the Longfellow Copper Company, in 1872 near Morenci, contained about 20 percent copper.

A century later, however, that same deposit produced ore averaging less than one percent copper. Where it was once possible, in Arizona's early statehood, to reap 100 to 200 pounds of metal per ton of ore (approximately five to ten percent copper), such high yields are but distant memories. Today, the average mine produces only 10 pounds of copper per ton of ore. Even that does not come easily. To obtain one ton of ore, the average mine must move an additional two tons of barren rock.

This diagram depicts the two primary copper processing methods used in Arizona.

Technology Continues the Trend
Because of the innovation and ingenuity of millers, and despite the lower yields of today's mines, the world's copper resources remain abundant. Throughout the world, including in Arizona, mining companies are constantly discovering new and better ways to extract, process and produce copper and related minerals. As a result of these efficient processes, only about one-fourth of one percent of Arizona's land area is actually utilized by copper companies in their mining operations.

Copper is used to mint a variety of coins all over the globe.

Discovering the copper ore imbedded in the earth and rocks of Arizona is no easy task. It takes a team of highly trained geologists, geochemists and geophysicists, along with sophisticated testing methods and instrumentation to locate this hidden treasure.

Once deposits are found, mining companies must blast and dig their way to the source. Working in Arizona's approximately 12 operating copper mines, both open-pit and underground, miners then carefully separate the ore from the waste material. Huge trucks move up to 240-tons of ore, which is dumped into crushers and broken into pieces ranging from the size of a walnut to that of a softball.

It is important to differentiate between sulfide ore and leachable ore. Generally speaking, sulfide ore is composed of minerals containing copper, iron and sulfur, hence the name sulfide. Leachable ore is composed primarily of minerals containing copper oxide.

Sulfide Ore — A Grinding Process
sulfide ore The next step after crushing for sulfide ore is grinding. The process involves running crushed ore through large, rotating, cylindrical machines called mills until it becomes a fine powder similar to flour or talcum powder. This powder is mixed with water and chemicals to create a slurry that is piped into flotation tanks. Here, particles of copper called copper concentrate, with a copper content of 25 to 30 percent, float up and over the edge of the tanks, while the waste material, tailings, sinks to the bottom for easy removal.

The copper concentrate is then smelted for the purpose of separating the elements — copper, iron and sulfur. The iron is removed from the furnace as slag, the sulfur in the form of sulfur dioxide is processed into sulfuric acid. The copper leaves the smelter in anode form — 99 percent pure. Anode copper is further processed through an electrolytic refinery where impurities are removed, upgrading the purity to 99.9 percent.

Oxide Ores — A Smart Solution
sulfide ore Extracting copper from oxide ores typically involves spraying the crushed ore with a sulfuric acid solution to dissolve the copper. In heap leaching, large piles of oxide ore are placed on impermeable pads and are sprayed with leach solution by a sprinkler system. The leach solution percolates down through the heap over time, picking up copper as it travels along. A central drainage system collects the run-off at the bottom of the heap.

The method used for recovering copper from the leach solution collected at the bottom of the leach heap is the SX/EW or solvent extraction electrowinning process. The solvent extraction (SX) part of the process includes a process of ion exchange between two solutions. During the ion exchange, a lighter organic solution floats on top of the heavier leach solution, much like oil floats on water. The copper atoms in the leach solution are extracted by the organic solution in a chemical exchange in which atoms go where they have the greatest chemical affinity. Once the leach solution is "emptied" of copper atoms, it is recycled back to the heaps for further leaching. The copper exchange is reversed in another tank that strips the copper from the organic solution and has a copper concentration approaching eight percent.