Unforgiving Ground

The Phoenix Mine in northern Nevada, USA, has ample reserves of gold, copper and silver. It also has something not quite so precious ? quartzite rock that is among the most abrasive of its type in the world. Newmont Gold Corporation, one of the world?s largest gold producers, started operations at Phoenix in 2006. Considering the extremely diffi cult ground conditions, it was among the toughest challenge the planners had ever faced.

?Anything that touches Phoenix rock wears fast,? says Mine Manager Mark Evatz. ?But the Pit Viper is big and bad and can take it.?

Evatz is referring to the fleet of six  Atlas Copco Pit Viper 271 blasthole dril at work in the pit. The tough rock conditons require down-the-hole hammer drilling and the Pit Viper drills are equipped with Secoroc TD 65 downhole hammers, 165 mm (6¾ in) bits and 1,450 cfm, 350 psi oil-flooded air compressors. An Atlas Copco DML and a DM45 midrange blasthole rig are also included in the fleet.

The mine?s goal is to keep approximately four million tonnes of muck in inventory to stay ahead of the shovels and support operational flexibility.

Drilling efficiency has been a priority for continuous improvement since operations began. The 16.5 m (55 ft) single pass depth capability of the PV-271 has contributed to this. Originally, the plan called for 20 ft benches, and 23 ft drill depths but the time spent moving from hole to hole had a negative impact on productivity. That plan resulted in drilling an average of 47 ft per hour. When drill depths were changed to 44 ft, supporting the blasting of 40 ft benches, the mine was able to utilize the single pass capacity of the PV-271 and performance increased to more than 60 ft per hour. Other aspects of continuous improvement, such as better knowledge of how the Pit Viper drills, have also helped to improve productivity.

?We are below our budgeted drill costs,? says Evatz. ?This is partially because the best cost-per-foot comes from hammer drilling when in hard rock.?

Pat McAmis, General Foreman, Maintenance Planning, agrees. He says: ?You can try to put more drills on the bench, but space and costs don?t make that practical.?

The mine focuses on maximizing the fragmentation of blasted rock while maintaining a minimuim dilution. Although the crusher can handle 30-inch boulders, McAmis says: ?The goal is to maximize what you?re digging ? keeping a methodical approach.?