Cullinan Mine’s Cat R1300G load-haul-dump fleet sets a new industry benchmark for availability.
Working continuously within Cullinan Diamond Mine’s intricate block cave network is a dedicated fleet of Cat load-haul-dumpers (LHD’s) that form the backbone of the production programme at the world’s second largest indicated diamond resource by in-situ value. Current estimates place this figure at around 204 million carats (including tailings).
The mine, situated some 40km distant from Pretoria, is now owned by the Petra Diamonds Cullinan Consortium following a R1 billion acquisition from De Beers in July 2008. Major growth plans are in the pipeline.
First starting out as an opencast operation in 1903, when the pit reached a depth of 189 m in the late 60’s the production programme went underground and mining is presently progressing on the B-Cut levels at a maximum depth of 747 m. (There are proven reserves up to 1 200m.)
A very distinctive mine, Cullinan is renowned for its rare and flawless blue diamonds (the blue colour derives from the borat geological composition), and first stunned the world with the discovery of the famed Cullinan Diamond in 1905. Weighing 3 106 carats rough, this stone still holds the record as the world’s largest gem diamond ever found.
“For every 100 tonnes that we mine, we take out approximately 39,5 carats,” says Arie van Wyk, Cullinan’s underground engineering manager, providing an indication of the richness of the kimberlite deposit.
Given the significance then of the Cullinan operation to the global diamond market, it reinforces the importance of having the right production methodologies and machines in place, and it is here that the mine’s thirteen Cat LHD’s play a pivotal role.
HERRINGBONE LAYOUT
These Cat units work up and down Cullinan’s 16 major working tunnels, formed in a herringbone pattern layout and providing access to upwards of 250 draw points, or block caves. They are constantly worked by the LHD’s, loading and hauling away the ore that moves downwards under gravitational forces.
Currently, the mine runs on a five day, two shift system, with the daily tonnage target set at around 10 000 tonnes.
Since there are no standby units, every Cat R1300G, with its estimated tramming capacity of 6.8 tonnes, is expected to meet its daily targets, travelling back and forth from the draw points to feed the underground crushing stations.
Each LHD records around 3 000 hours annually and there are now four older machines in the fleet which have accumulated between 18 000 and 20 000 hours. As Nico Coetsee, Cullinan’s maintenance overseer for trackless production points out, these high hours have been achieved without any major mechanical intervention beyond routine servicing and maintenance.
“Worldwide, the general norm for an LHD is to rebuild major components, like engines and drive trains, at 5 000 hours,” explains Coetsee, “so achieving in excess of 18 000 hours without having to do so is truly remarkable.”
Prior to switching to Caterpillar, Cullinan tended to scrap its LHD’s at around 12 000 hours. However, the introduction of the Cat R1300G has shifted the mine’s benchmark on mechanical life expectations. Coetsee says Cat availabilities, starting out at around 98% when new, now average around 86% on the older 18 000 hour plus LHD’s, which is still excellent.
“We have over 150 vehicles underground so you need to be disciplined about predictive and preventative maintenance schedules, plus the production and engineering teams must work in the same direction, which is what we’ve achieved with great success at Cullinan,” says Coetsee, adding that operator training is equally important to ensure machine longevity.
Every day between 05h00 and 08h00, production takes a break and this is the time when the LHD’s come in for their scheduled services.
Using a maintenance backlogging system, all the part items required for any specific job are preordered as a kit so the components are always there beforehand and the time planned for the job predetermined. For Cullinan this means that the mine can commit to tonnage targets with confidence.
“Mechanisation and personnel efficiencies are the key drivers underground to ensure safe and rapid materials transport,” adds van Wyk. “For example, we’re phasing out the locomotives, and the incline conveyors are being replaced with horizontal conveyors in the new mine design.”
Moving forward, Petra is expanding its underground mining footprint. This will take Cullinan’s production from just over 907 000 carats in the 2011 financial year to 2,4 million carats by 2019.
Supporting these increasing volumes will be the mine’s growing Cat LHD fleet. This includes the addition of larger 10,2 tonne capacity Cat R1600G’s as the mine ramps up to a three shift system and develops new, larger tunnel systems.
