Copper Mining and Production

In the beginning mining was a very simple and exhaustive activity. In early civilizations, slaves were used to do the backbreaking labor of breaking up the rock layers to find copper and other minerals and then removing the copper from the small tunnels and pits where it was found. These early efforts at mining developed very slowly because the technologies available to society were very limited. The first real breakthrough from the stage in which native copper was hammered and shaped came with the discovery of the process of smelting.

The ability to heat copper-bearing ore in a charcoal furnace to a high enough temperature to melt it, allowed metalsmiths to purify the copper to a much greater degree and allowed them to pour molten copper into molds of various shapes and sizes to improve the weapons, implements and art objects they designed and manufactured. This advance in smelting also led quickly to the ability to alloy copper first with tin to form bronze, and then with zinc to form brass. Both of these new alloys were harder and more durable than copper.

With the advances in smelting and the increased use of bronze and brass, the need for copper increased significantly and so did the search for new supplies of ore. One of the first major mine sites in the world was developed at Rio Tinto in Spain in the year 3000 BC to mine copper, gold and silver. This mine is still active today, 5000 years later partly due to the fact that technology of mining and refining copper has advanced continuously over the past five millennia.

Copper mining today has evolved into a very scientific, long term and expensive process that occurs in four basic steps: 1) Exploration; 2) Mine Development; 3) Production; and 4) Long-Term Reclamation. These four stages of development have been necessary from the beginning of mining but are better defined now that mining has become such an enormous enterprise. In early American history, native peoples mined copper and other metals from the hills and mountains of North America. These efforts, like those of the early European settlers, were generally through one-man operations consisting of a small hole in the side of a mountain or hill and the limitation of simple tools and a great deal of labor. Today, the number of active copper mines in the United States is roughly only 20 compared to the past in which were thousands of "one mule" operations.



This chart, Fig. 1, illustrates the cost and time to develop a medium-sized copper mine. Today, the demand for copper as a commodity has grown to a point so that every year there is a need for 10,000,000,000 pounds of copper worldwide, and the size of the mines and the tremendous technology required to develop them is enormous.

Copper ore occurs in two basic forms in nature: sulfide ore and oxide ore. In order to extract the copper from the rock, where it often represents less than 1% of the rock material, different processes are used.

Copper sulfide ore is a natural mixture of rocks containing copper, iron and sulfur. This mixture requires a grinding process to separate the copper from the rest of the materials. The steps in the process are as follows:

	blasting and hauling of the copper ore to the mill
	grinding and pulverizing of the ore to a fine powder
	separation of the copper from the other basic rock substances through flotation (25 - 30% pure copper)
	smelting in a furnace to separate the iron and sulfur from the copper (99% pure copper)
	final purification to 99.9+% pure copper using an electrolytic process

Copper oxide ores are ores that contains copper and other minerals in oxide form and require a somewhat simpler and newer refining process.

	It starts with blasting and hauling of the copper ore to large piles called heaps.
	These piles or heaps are created over leak-proof pads; and the piles are sprayed with a mild sulfuric acid solution, the first step in the solvent extraction/electrowinning process (SX/EW).
	As the acid solution percolates through the pile of ore, it picks up copper molecules.
	The solution drains out the bottom of the heap into pipes and is separated with the acid being returned to the top of the heap (8% pure copper).
	The final step is the electrowinning (EW) portion of the process, and through an electrolytic process, 99.9+% pure copper is captured on cathode sheets.

There are three primary methods of mining minerals and other metal ores from the earth: A) Surface mining; B) Quarrying; and C) Underground mining. The following diagram, Fig. 2, illustrates these three methods. In Arizona copper mining, the surface mine approach is the most common; and the Morenci Mine in eastern Arizona is the largest surface mine in North America.

Copper mining has developed as a high tech industry because of society's need for ever larger quantities of copper to build and develop products. A global positioning satellite system (GPS) and sophisticated helicopters and geological mapping equipment are now used to do early exploration. Drills that can bore horizontal and vertical holes over a mile long are used to take samples of potential ore bodies. Trucks and huge electric shovels designed just for mines are used to move hundreds of tons of rock and ore in one load. Grinding mills and sophisticated extraction processes like SX/EW have been developed to move millions of tons of rock and ore through the refining process to yield virtually pure copper. Computer programs have been developed to link direct milling operations, control mining traffic in surface mines, and move cubic miles of air in underground mines.