The open pit gold mine of La Herradura Penmont in the northern state of Sonora, not far from the U.S. border, is improving its productivity through a combination of upgraded drill rigs and new rock drilling tools.
The La Herradura Penmont Mine, which is jointly owned by Fresnillo plc and Newmont USA, has been successfully mining its gold since it opened in 1996.
Current production is around 190 million tonnes a year, largely due to the productivity of its DM 45 HP (high pressure) drill rigs from Atlas Copco, and more recently, a transition to the larger DML HP. Now the mine is making further improvements by introducing new rock drilling tools.
Following successful tests with two Atlas Copco QL 85, DTH (down-the-hole hammers) equipped with 216 mm bits, the mine has decided to switch to the “golden hammers” along with rotary drill pipes and accessories from Atlas Copco Thiessen.
Drilling in gneiss quartz cuadrostatic rock, the DML rigs increased their penetration rate by 15–20 percent thanks to the hammer.
According to Carlos Alberto Torres Gamez, Mine Drill and Blast Chief, the service life of the hammer also increased by 30 percent compared with the previous equipment. As a testimony to the performance of the equipment, this combination is now to be used throughout the operation by La Herradura contractor SECOPSA, one of Mexico’s leading open pit mining contractors. According to Mine Manager Jose Arturo Arredondo Morales, Fresnillo’s trust in the Atlas Copco brand lies at the heart of La Herradura’s success. He says: “We benefit from Atlas Copco’s quality products, support and commitment.”
Although the DM45 HP is capable of drilling the desired 8 m bench height, opting for the larger DML HP allowed the mine to increase the hole diameter to 216 mm.
The holes are drilled in a 5.5 m by 6.5 m pattern to a total depth of 9.2 m, including 1.2 m of subdrilling.
An Atlas Copco ROC L8 (now named FlexiROC D60) is used to drill 140 mm diameter presplit holes on double benches with a total depth of 16 m. The penetration rate averages 34 m per hour/rig and an average production of 28 holes or 2 520 meters drilled per shift. The waste-to-ore ratio is 3–1, producing 0.5 million ounces of gold in 2011.
Getting ready for growth
The mine has five pits in operation and a new sulphite processing facility is being built to process better quality ore while a new underground area named Centauro Bajo is being developed below the Centauro Alto pit. In addition a new open pit, Noche Buena, will be added.
The Centauro Alto pit is now at 250 m and it is estimated that it will reach 500 m in eight years. Underground Mine Manager Hector Contreras says underground operations will continue from there. “This mine has another 15 years in it and exploration is continuing. We don’t know the true extent of the reserves yet,” he says.
Equipment for the development process arrived in April 2012. This includes two Atlas Copco Boomer S1 D face drilling rigs, one Atlas Copco Boltec rock bolting rig and three Atlas Copco Scooptram ST1030 underground. The mine also has an Atlas Copco Robbins 73RH raiseboring machine.