Just a few months after project completion along the west face of the Andes Mountains in Chile, the three sites that make up the Los Bronces copper concentrator expansion have begun to blend into the dramatic landscape once again. Completed by Bechtel in late 2011, the spectacular and complicated $2.8 billion project crosses many miles of rugged mountain terrain and extreme altitude variations, and has doubled copper mining capacity in the Los Bronces district for customer Anglo American.
The highest and largest project site was at Confluencia, two miles (3.2 kilometers) above sea level, where Bechtel terraced and leveled the steep rocky pinnacle between two gorges to create space for the grinding facility. Upstream of the grinding building, the team built a conveyor through a 2.7-mile- (4.3-kilometer-) long tunnel, driven by another contractor through an adjoining mountain, to bring coarse ore for grinding from the customer’s established Los Bronces mine.
Unique safety precautions
High-altitude sites like Confluencia mean big challenges, due to the effects of altitude on workers, weather, potential avalanches, and extremely rugged terrain. For safety, Bechtel required all workers on the project to pass strict medical exams. Some agreed to special diets in order lose weight and reduce their blood pressure before they could start work. Yet, subject to official confirmation, Bechtel’s project team appears to have set a national record for safe work performance.
Altitude posed other challenges, too. Bechtel managed deliveries of materials and equipment up narrow mountain roads to Confluencia under heavy winter conditions, with snow that piled nearly 13 feet (4 meters) high. To ensure driver safety in such harsh conditions, the project’s Winter Committee assessed roads for avalanches and other risks 24/7. The 2009 global financial crisis, Chile’s massive earthquake in February 2010, significant geotechnical issues, and unexploded ordnance added to the team’s challenges.
A steep vertical connection
The second of the project’s three work sites is a 34-mile- (54-kilometer-) long, slurry transport and reclaim water pipeline system linking Confluencia to the project’s third site—a flotation plant built on a former military target range 8,694 feet (2,650 meters) lower, at Las Tortolas. That’s where ore ground at Confluencia is converted into copper concentrate, the raw material for copper smelting.
The slurry pipeline carries ore from the grinding facility to the flotation plant along a twisted path—under rugged terrain, through mountain tunnels, and via bridges crossing deep canyons. The elevation drop posed a challenge for engineers designing the downhill slurry pipeline. With such a strong gravitational pull, the system required five “choke stations” to dissipate energy, reduce pressure, and control the slurry flow.
A water reclaim system follows the same route as the ore pipeline, but carries reclaimed slurry water from Las Tortolas back up to Confluencia, using the power of five pump stations. The system is an important part of Anglo American’s water management and sustainability strategy.
Los Bronces was a huge project that required 48 million job hours and more than 14,000 workers, most of them Chilean, and most of them housed and fed in well-equipped Bechtel-managed work camps.
At the Las Tortolas site, the new flotation facility is tucked into a hillside adjacent an existing flotation plant. The project team removed 3.5 million cubic meters (4.6 million cubic yards) of rock and earth from a former military target range. Visit the photo gallery for more images of Los Bronces.