Availability is key: CC&V demands consistent production from haulage fleet
Cripple Creek & Victor Gold Mining Company operations run around the clock on every day of the year. About 300 full-time employees and 50 contractors work 12-hour shifts to produce 163000 tonnes (180,000 short tons) of ore per day. Four crews in each department are required to provide coverage throughout the year.
The ability of these employees to meet their production targets is largely dependent on the availability of the mining machines they operate. The site relies heavily on consistent production from its haulage fleet and work can come to a standstill if a machine breaks down. The mine operates a fleet of Cat 793D trucks, and as it began looking to expand its fleet, agreed to be a field follow site for the new Cat 793F.
A historic gold mine
Cripple Creek & Victor Gold Mining Company mine (CC&V) is a joint venture majority owned and operated by AngloGold Ashanti (Colorado) Corp. The current mining operation, started in 1994, is called the Cresson Project. The site south of Denver, Colorado, USA, had been mined using underground methods since the late 1890s and into the 1950s. The area is famous for the great gold find of the district, the “Cresson Vug,” a cavity in the rock, lined with crystals somewhat like a geode, where gold was essentially picked from the walls of a room-sized void encountered about 366 meters (1,200 feet) below the surface in 1914.
Engineering for the modern Cresson mine began in 1993. Obtaining the various permits necessary to mine was completed in 1994. The first Cresson gold was poured in 1995, and an expansion construction began in 2000. In late 2003, CC&V reached its planned expansion capacity of 18.1 million tonnes (20 million short tons). The mine poured its two millionth ounce in 2004.
As of December 2009, the mine reported a proven ore reserve of about 112.5 million tonnes (124 million short tons), containing approximately 1.6 million ounces (45.5 million grams) of recoverable gold. The annual gold production rate from the Cresson Project varies somewhat with about 250,000 troy ounces produced in 2008. Currently, the mine life is estimated to last until 2016.
This low-grade, open-pit operation produces doré that is 70 percent gold and 20 percent silver. CC&V processes about 22 million tonnes (24 million short tons) of ore per year. The ore is treated using a valley-type, heap-leach process with activated carbon used to recover the gold. The resulting doré buttons are shipped to a refinery for final processing.
Evaluating haul trucks
Buying a mining truck is serious business. Not only is there the substantial outlay of money to consider, but there are also the myriad ways that truck will impact operations on the site. From matching with shovels, to fitting on the haul road, to handling high altitudes — many variables combine to determine the right truck for the site. And it’s imperative to strive for the lowest cost-per-tonne possible to succeed in the competitive gold mining business.
When it was time to add some new trucks to the CC&V fleet, the site began an evaluation process that lasted nearly six months. “We did extensive studies on a number of manufacturers’ trucks,” says Vivien Hui, a senior engineer in mine operations for AngloGold Ashanti (Colorado) Corp. “We looked at everything you can think of — from evaluating the engine block material to gauge its ability to handle our site’s rough terrain, to evaluating the ease of maintenance on the drive system.”
The site evaluated dozens of variables, including how the truck options matched the site’s current shovels and how the truck fit with the site’s infrastructure, which requires travel from the shop, to load-out, to bin, to crusher. The site considered the overall capital cost for each truck, the costs for planned maintenance and major components, and the cost for labor required to maintain them.
The mine looked at all variables first by cost-per-hour, then used a modeling program called Q’PIT to measure each option on a cost-per-tonne basis. “We fed the details into the model and it told us the cost-per-tonne over the life of our specific mine,” says Hui.
Considering size options
One might think that in order to get the most production from a site, the haulage fleet should be the largest size trucks possible. That wasn’t true in the case of CC&V.
“We evaluated the ultra class trucks over 360 tons,” says Hui. “And we found that for our mine, the larger trucks would actually result in a higher cost-per-tonne than a smaller truck.”
There are a number of reasons why:
Haul profile. The site has both uphill and downhill loaded haul roads and judged the trucks by the cost-per-tonne based on both of these profiles.
Infrastructure. Going with a large truck would have made it necessary to expand the road width in order to meet the CC&V standard requiring roads that are just over three times the width of the truck.
Dilution. Considering the dilution in its average ore grade, it was determined that the additional waste material would reduce the advantages gained from using a larger truck.
Tires. As trucks get larger, exponentially the tires get more expensive. CC&V considered its relationship with tire manufacturers and the allocation of available tires.
Shovels. Shovels currently on site were not the right size to be the most productive with larger trucks.
Testing a new model
When Caterpillar approached CC&V to consider being a field follow site for its new F-Series trucks, the timing couldn’t have been better. The site was able to evaluate this new and improved truck in the midst of its search for new trucks to add to its haulage fleet.
The site was happy with its existing fleet of 227-tonne (250-ton) 793D trucks and agreed to test two of the 793F trucks. The fifth generation of the 793 has a powerful new engine, choice of power train options, choice of body systems and a completely redesigned operator station. Serviceability has been updated with more ground level service points and 1,000-hour hydraulic filter service intervals. Other changes promote safe operator and technician access — wider walkways, flat upper deck, rear access ladder and three-way lock-out tag-out box mounted on the bumper.
“We short-listed down to three trucks that we were considering, and then we narrowed it even further to the Cat 793 trucks,” says Hui. “We had a combined 15,000 hours to study the new F-Series, and after the field follow we purchased both trucks.”
Hui reports that the F-Series met the site’s cost-per-tonne criteria and the capital cost comparison was favorable. While all of the F-Series enhancements are important, there are several that are of particular importance to CC&V.
The 793F’s new engine is a great match for the environment in the Cripple Creek mining district, reports Bruce Neldner, parts and service manager at Cat dealer Wagner Equipment, which is responsible for the Cat equipment at the Cresson Project.
“This mine is on the side of a mountain, and there is a huge elevation change from top to bottom,” he explains.“They’re working at 3048 to 3350 meters (10,000 to 11,000 feet) altitude. The less air there is, the less fuel you can use, which means less power. But with this engine, you don’t have to cut the fuel in the higher elevations.”
Hui agrees that it’s very important that the engine doesn’t derate at the mine’s altitude. “We get the same horsepower at 2 miles high as we do at 1 mile high,” she says.
The 16-cylinder, 1976-kilowatt (2,650-horsepower) Cat C175-16 diesel engine displaces 5.3 liters (323 in3) per cylinder, for a total displacement of 85 liters (5,187 in3). The 793F delivers 174 kilowatts (234 horsepower) more than its predecessor, the 793D.
The engine redesign was done in part to meet Tier 2 emissions requirements; however, CC&V has found a number of additional benefits. “We found that, yes, they redesigned the engine to be better for the environment,” says Hui. “But we’ve also learned that the new block material is stronger, which is great for our hard rock environment. And performance went up in the process.”
The 793F delivers more power to the ground, explains David Rea, a product marketing specialist in Caterpillar’s Global Mining division. “It’s faster on grade, and because mining trucks spend the majority of their time on grade, it can travel faster, move more tonnes, and deliver a lower cost-per-tonne,” he says.
Hui reports the truck is a good match for the site’s haul profile. “It goes fast uphill and fast downhill. It has great retarding going down and good torque and speed going up. This reduces our cycle time.”
Operator Vic Hines, who has been an operator at CC&V for eight years, is impressed with the truck’s performance. “The new engine and torque converter are super,” he says. “It takes the hills great and takes off good on the grades. The throttle locks and retarder set are really nice — I use them every round. It works like a cruise control going downhill.”
Cat uses oil-cooled multiple disc brakes on all four wheels. They provide immediate, fade resistant braking and retarding and with proper attention to oil temperatures, the brake discs and plates experience virtually no wear. Four-wheel balanced braking improves handling and machine control.
Another advantage is that unlike some trucks, the Cat engine and truck are made by the same manufacturer. “They’re designed to work well together and we only have one manufacturer to deal with if there is an issue,” Hui says.
Safety and comfort
The new cab in the Cat F-Series trucks features a number of improvements to make it a more comfortable working environment, including controls and gauges that are positioned to maximize productivity and minimize fatigue.
Hines says he appreciates the smooth, comfortable ride and the improved visibility due to more window area. “The cab is roomy and all the controls are reachable,” he says. “The comfort is great.”
The safety enhancements of the new truck, such as improved access and eggress, are also appreciated by the operators. “Caterpillar definitely thought about safety when they designed the F-Series,” says Hui. “It’s a number one goal for us and they are helping us achieve it.”
A number of the changes in the 793F were done to make it easier to service — a welcome improvement for the dealer and site technicians who work on the trucks. The operators also appreciate that walk-around inspections are easier.
“The oil checks and hubs are nice and the air bleed system is easy to access,” says Hines. “The sights on the tanks are also improved.”
Wagner performs most of the maintenance on the Cat equipment at the Cresson Project, although CC&V does much of their own planned maintenance on site. “Overall we’ve found the new truck easier to service,” says Neldner. “A lot of the improvements are concentrated on the service points. Having as many at ground level as possible makes them easier to access. It’s also safer because the less you crawl around on the machine, obviously the safer you are.”
CC&V also was impressed by the new frame on the 793F. Cat frames use a high strength, low alloy (mild) steel with castings in highly stressed areas. A key advantage of mild steel frames is that they can be easily welded in the field. They’re designed to last in rugged mining environments.
“The percentage of castings went up, so the frame has more durability,” says Hui. Frame life is important because it dictates the long-term economic life of the machine. “We know we can keep rebuilding this truck and its components as long as the frame lasts,” she says. “This new frame gives us confidence that we can run the truck to or even past the life of our mine.”
Technology also weighed heavily on CC&V’s decision to purchase the F-Series field follow trucks — in particular, the upgraded VIMS technology. VIMS collects and transmits machine data and turns it into valuable information used to track productivity, machine performance, service scheduling, trends, diagnostics and equipment condition monitoring.
“There were third party technologies that do the same thing, but we like that it’s integrated into the truck,” says Hui.
The third generation of the system — VIMS3G — offers enhanced convenience and functionality, along with updated communications capabilities. A real-time browser allows users to view machine data on up to 10 machine parameters in an easy-to-access Web browser. “Plenty of technologies can capture the data, but this is realtime, which makes it much more useful,” says Hui. CC&V partners with Wagner to analyze the data, review trends and develop predictive maintenance plans.
Many variables are weighed when considering the purchase of a new truck, and one of the most important is availability. “We need our trucks to be running in order to meet our production goals,” says Hui. CC&V counts on Wagner’s existing support structure to make sure the fleet delivers high availability.
“Our mine superintendent would agree that the support of the dealer is one of the most important things in our decision to purchase Cat trucks,” says Hui. “This consistent support — from both Caterpillar and the dealer — helps us stay on budget. We could maybe buy products with a slightly lower cost-per-tonne on paper, but if we can’t count on them, then they’re not giving us that consistency we need to meet our targets.”
Wagner’s Neldner says the dealership has worked hard to earn the mine’s trust. “They have to know that their trucks are going to be supported,” he says. “We have a lot of Cat equipment there and our support is proven to them. We have a good, healthy relationship.”
Hui says the support the mine receives from Wagner is second to none. “We’ve built a relationship where we are working together to make things happen and to fix problems,” she says. “There’s no finger-pointing when something goes wrong. It’s Caterpillar, Wagner and us, working together.”