How the Pit was Made

How the Pit was Made. . The pit was created bit by bit over a period of almost 60 years, through three mining phases: , 1. The Sacramento Pit (mined 1917-1929) , 2. The Lavender Pit (mined 1950s-1970s) , 3. The Holbrook Extension (mined late 1960s-1970s), Mining the open pit , The pit was mined by way of a series of 50-foot-high "benches" or steps cut into the edge of the ore deposit. , A: Closely spaced holes were drilled into the benches and filled with explosives. , B: Explosives were detonated, breaking up a layer of rock. , C: Broken rock was shoveled up and hauled away. The older Sacramento Pit used steam shovels and ore cars on railway tracks. The newer Lavender Pit used electric shovels and haul trucks. , D: Ore went to the crusher for further processing. Waste rock (rock containing little or no copper) was hauled away., Bigger , Over the years, open-pit mining required bigger and bigger shovels and haul trucks. By moving larger quantities of rock, mining operators could cut costs. Bigger machines also meant that fewer workers were needed. In 1954 the haul trucks at the Lavender Pit could hold 35 tons of rock. By 1974 the trucks could hold 65 tons. Today, typical haul trucks in Arizona copper mining carry 260 tons or more., ... BRECOME "ORE"? It's all a matter of economics and ... or if the process of extracting the metal costs too much, mining people call it "waste rock." But if metal prices rise, or if cheaper methods of extraction are invented, that "waste rock" may become "ore." (below: Sacramento Hill operations, 1920), SPIRAL ROADS: Spiral roads that intersect mining benches were routes used by trucks hauling copper ore or waste material. Waste material went to the No. 7 Stockpile. Ore was sent to the crusher, then carried by conveyor belt to the concentrating mill across the highway. All of these processing facilities were removed and remediated after the mine closed. (below: Bisbee open-pit operations overview, 1974)