This is a regular column which attempts to answer frequently asked questions about mining in the area.
What is mined in the area and how is it mined?
The primary metals mined in our region include copper, smaller amounts of molybdenum, and trace amounts of gold and silver.
Many mines in the area started as underground mines and then became open pit mines. Mine engineers and geologists evaluate ore bodies and determine whether it is more cost effective to mine the ore by underground or open pit methods.
We have both open pit mining (Pinto Valley) and underground mining operations (Resolution Copper) in the region, plus a smelter for processing the copper (FMI and one of only 3 smelters in the US).
FMI also operates and a rod plant for converting copper to cathodes used in a wide range of manufacturing operations. BHP runs a leaching plant for extracting metals from ore with acid.
Ore (rock which contains valuable metals) is mined from the ground by blasting and loading broken rock into haul trucks for processing. The two primary methods of processing copper ore are milling/floatation and leaching. In the Globe Miami area, both methods are used.
In this process, mill grade ore is sent to the mill where the rock is crushed and finely ground so the copper can be separated from the barren waste rock by floatation. The concentrator building holds a series of floatation tanks where reagents and water are added to the finely ground copper ore which is then further refined into pure copper at the smelter.
In the floatation circuit, the ground rock that does not contain desirable metal is slurried out in a series of pipes to a tailings storage area that will eventually be reclaimed and revegetated at the end of the life of the mine.
Leaching is an entirely separate process. Ore considered suitable for leaching is hauled by truck and placed on a leach pile. A solution of weak sulfuric acid is sprayed on the top and sides of the pile so it can percolate through the broken ore and be collected in ponds at the bottom.
This mixture is then pumped to a Solvent Extraction/Electro Winning plant (SXEW) where it is further processed to make pure copper sheets called cathodes which are 99.99999% pure copper. (BHP)