In the heart of the mine

AngloGold Ashanti invests R$ 65 million in mobile equipment to increase the productivity in one of its main gold-extracting operations in Brazil

The third largest world producer of gold, AngloGold Ashanti works in 11 countries, having 21 active operations. Brazil occupies a special place in this portfolio, being responsible by ten percent of the total world production in 2013, what corresponds to 529 thousand ounces of this metal. This volume represents approximately 15 tons and an income of approximately 681 million dollars (calculated by the average price of the metal). In this country, the operation includes four extracting plants, located in the states of Goiás (Serra Grande) and Minas Gerais (Santa Bárbara, Lamego e Cuiabá). The underground mine of Cuiabá—located in the city of Sabará, in the ferriferous four-side—stands out in the country operations. In this mine, the extracting process is being improved, demanding heavy investments in equipment and technology, as M&T reporters went to check.

During the last three years, Cuiabá received investments of R$ 341 million, being R$ 65 million in mobile equipment. The focus was the expansion of the underground cave, currently in the sublevel 18, what corresponds to approximately 1200 meters of vertical depth. But the planned and approved expansion of excavation is reaching the sublevel 24, more than two kilometers deep. “Currently, the studies include excavation up to the sublevel 32 which will be defined and planned by the board of directors during the next years”, says Alessandro Pacheco de Souza, mobile equipment maintenance manager of the Cuiabá Mine.

But the Cuiabá Mine does not draw the attention only by its depth. With the recent investments, its operation was improved with a larger use of the process of excavation by sublevels. “Currently, 63 percent of our production is carried out using the Sublevel Bench Method, what represents a significant evolution due to the new technologies and equipment purchased by us”, comments Souza, informing that till three years ago the extraction was developed using the cut and filling method, which is less safe and efficient, what leaded to its replacement.

FLEET

In the sublevel method of mining, drilling is carried out by fan drills and drilling jumbos. In the case of the Cuiabá Mine, blasted material is transported by low-profile loaders and off-road trucks. Since it is an underground mine with longitudinal layout in several extracting points, LHDs with remote control are also used to ensure the operators’ integrity. The total fleet currently used in the mine includes nine LHDs of various models, all manufactured by Caterpillar.

In fact, mobile equipment was one of the assets that received more investments during the last three years, mainly the articulated trucks of 30 and 45 tons. “We have six units of the first model and seven of the second model, all manufactured by Caterpillar”, details Souza.

Drilling is carried out by seven two-arm and five solo Sandvik jumbos. Scaling (removal of rock pieces that became loose after blasting) is also carried out by special machines, the scalers. There are five units currently operating in the Cuiabá Mine, together with ten work platforms used to load explosive in the holes and to carry out supporting works. The supporting fleet has also motor graders, backhoes, loaders (for removal of sterile material) and lubrication and fuel supply trucks. There is also a third-part fleet of 6x4 road trucks mainly used to transport sterile waste material.

The current fleet of the mining company includes 94 machines. Most of them were bought in the last three years, attending to a plan of fleet renewal and justifying the investment of R$ 65 million. The demand by renewal is defined for the entire fleet according to the monitoring of equipment’s life cycle by the manager and his team. In this process, the traditional process of fleet availability, the reliability—through the analysis of Mean Time Between Failures (MTBF)—and the maintenance cost per working hour are also evaluated.