Australian, Bolivian and Japanese know-how have come together for a collaborative production trial at one of South America’s true mining giants.
Technology developed by Australia’s Cooperative Research Centre for Optimising Resource Extraction (CRC ORE) has been successfully implemented at the Sumitomo-owned San Cristóbal mine in Nor Lípez, southwest Bolivia.
Called Minera San Cristóbal in Spanish, it is the largest mine in the country and one of the world’s largest deposits for zinc, lead and silver, producing around 1500 tonnes of zinc-silver and lead-silver concentrates a day.
San Cristóbal has been the beneficiary of a full scale production trial of Brisbane-based CRC ORE’s Grade Engineering technology since late 2018. The process helps to separate ore from waste before it enters the comminution phase by matching separation technologies to specific characteristics of the ore.
This can lead to a deeper understanding of the orebody and allow producers to exploit ore characteristics such as heterogeneity and variability, factors that are “typically overlooked in favour of maximising extraction rates and loading efficiency”, according to CRC ORE’s 2017 white paper on the subject.
CRC ORE and Sumitomo’s main aim for the project was to upgrade mineralised pit waste to detect a new economic stream that could be combined with run-of-mine feed through the concentrator to produce a positive net smelter return.
Results from the San Cristóbal trial have shown that 66 per cent of the produced value was found in just 25 per cent of the Grade Engineered mass. Energy reduction ranging between 15-20 percent has also been noted at the mine’s semi-autogenous grinding (SAG) mill when a combination of Grade Engineered and direct run-of-mine (ROM) feed has been used.
“Grade Engineering outcomes do not create ‘new’ metal but rather exchange metal from separated components between existing destinations to create improved net value after cost of exchange is considered,” the white paper explains.
“This involves exchanging a component of separated mill feed with other destinations such as mineralised waste, stockpiles or dump leach with low recovery.
“The aim is to bring metal forward from destinations that are not delivering maximum current value and reduce overall costs per unit metal produced.”
Grade Engineering methodology includes five technology options (levers) that are designed to work well with different kinds of rock.
Levers one and two are designed for size-based operation at the ROM and primary crushing stages; Levers three and four divert material at the truck or conveyor stage, while lever five is designed for coarse gravity separation after secondary crushing has commenced.
The technology is expected to reduce San Cristóbal’s energy consumption while delivering a considerable profit for the mine should the technology be fully implemented, according to CRC ORE operations director Tom King.
“The big benefit of Grade Engineering is its potential ability to extend the life of the mine and add over $451 million in profit to its value,” he explains.
CRC ORE’s technology was introduced to San Cristóbal in part because of owner Sumitomo’s presence as a participant of the Brisbane-based cooperative research centre through its subsidiary Summit Mining International.
A Metso Lokotrack ST2.8 mobile screening plant was utilised during the trial to help provide sufficient capacity (450 tonnes an hour) for production scale testing.
“So far, results show that by applying Grade Engineering to areas previously designated as ‘mineralised waste’, the value of Grade Engineered feed to the mill can be increased by over 2.5 times,” CRC ORE chief executive officer Ben Adair says.
“This has the potential to convert this waste material into high grade ore-feed with associated opportunity to increase metal production and reduce process power and water intensities.”