Copper and other metals form because of the dynamic geologic forces that have molded and shaped our planet since its beginning. These processes continue today, but because most of the time they happen at a very slow rate and at great depths, usually, we are unaware of them.
Metals and metallic mineral deposits occur where movement of the earth's plates allows hot fluids to chemically and mineralogically modify, or “alter” existing rocks. The fluids and heat cause elements to combine forming minerals that contain metals. Over time, weathering from water and wind at or near the earth's surface further affects the rocks. The combination of these natural processes formed many of Arizona's copper deposits. Because the copper deposits in Arizona often contain large and small crystals together, they are known as “porphyry” copper deposits.
Copper can be found all over the earth, but it is in abundance in relatively few places. Probably, the beautiful greens and blues of copper oxides first attracted man's eyes. Historical evidence shows that these minerals were ground into powder, mixed with animal fat, and used as body paint. In addition, on rare occasions, pure or “native” copper deposits were discovered as outcrops (places where the metal could be seen in rocks at the earth's surface). Most copper, though, is found in copper-bearing minerals that are usually found beneath the surface.
There are two main types of copper-bearing minerals — sulfides (those that contain sulfur and have not been affected by oxygen) and oxides (those that have been affected by oxygen and contain little or no sulfur). Typical sulfide copper minerals are bornite, chalcocite, chalcopyrite, and covellite. Oxide copper minerals include azurite, chrysocolla, cuprite, and malachite. Many copper-bearing rocks also contain molybdenite, lead, zinc, gold, platinum, nickel, iron, and silver. However, the potential of copper minerals probably would not be realized without people who have knowledge about the earth and the expertise to make use of that knowledge. |
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Geology is the science that deals with the physiology and natural history of the earth including the structure and development of its crust, the composition of its interior, individual rock types, and forms of life found as fossils. Using their knowledge about the earth, scientists known as geologists study rocks in an area, use surface and aerial maps and geophysical methods, and analyze samples taken from both the surface and below the ground to give them an idea of where there may be copper ore bodies. Once they have determined where a copper ore body may exist, geologists and mining engineers might begin planning a site for a future mine, but for every 20,000 prospects only 1 actually becomes a mine.
Some of the most important mines in Arizona are copper mines. This is because relatively late in geologic history, volcanic action provided the fluid, heat, and elements to concentrate copper in localized deposits in Arizona.
Even though Arizona is well known for copper, copper-bearing minerals are not found in abundance in every part of the state. Concentrated deposits of copper-bearing minerals occur mostly in what is known as the transition zone or “copper belt.” It crosses the state from northwest to southeast between the Colorado Plateau to the northeast and the basin and range region to the southwest.
Mineable copper ore bodies may contain as little as 0.2% copper, but because of modern technology, the metal can be extracted from rocks containing even these very small amounts. Today, the average mine produces only about 10 pounds of copper per ton of ore, and, on average, for each ton of ore, an additional two tons of barren rock, or overburden, must be moved.
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