Name of the Project
Cullinan processing plant project.

Location
Gauteng, South Africa.

Client
Petra Diamonds (74%), Kago Diamonds (14%) and the Itumeleng Petra Diamonds Employee Share Trust (12%).

Project Description
Petra Diamonds plans on building a modern, fit-for-purpose processing plant at Cullinan, with a throughput capacity of six-million tonnes a year.

The new plant is expected to improve the recovery of the full spectrum of diamonds, thereby increasing the volume of stones recovered and protecting large stones from breakage.

It will also improve the efficiency of the material flow, thereby significantly lowering operating costs.

The new plan will incorporate:
• autogenous milling – a gentler recovery process that breaks down ore using attrition rather than crushing, thereby better protecting the large, high-value stones for which the Cullinan mine is known;
• high-pressure grinding rolls technology – a gentler liberation technique incorporating interparticle crushing, thereby moving away from high-impact cone crushing; and
• XRF X-ray technology to replace conventional dense-media separation plants to treat coarser +12 mm material.

In addition to the benefits of large stone recoveries, the improved diamond liberation technologies outlined above are expected to lead to an increase of about 10% in the overall grade achieved at Cullinan.

Further, the new plant will reduce the processing footprint at Cullinan from about 27 ha to an estimated 4 ha, with the associated reduction of engineering infrastructure deployed, including an expected reduction in the number of conveyor belts used from 151 (spanning 15 km) to 22 (spanning 3 km).

The new plant is expected to yield a saving of between R20/t and R25/t in processing costs, owing to increased energy efficiency and improved water consumption, as well as reduced circulation and maintenance requirements.

No impact on current daily operations or throughput at Cullinan is expected while the new plant is being constructed.

Jobs to be Created
Not stated.

Net Present Value/Internal Rate of Return
The project has an internal rate of return of 25%, with a payback of about three years.

Value
The project will cost about R1.65-billion to implement.

Duration
The new plant is expected to be commissioned and fully operational in the fourth quarter of the 2017 financial year.

Latest Developments
The construction of the processing plant is nearing completion.

Commissioning of the plant started towards the end of the third quarter ended March 31, 2017, focusing on the first two mills and the electrical, water and slimes handling infrastructure.

Production through the old plant ceased in mid-April 2017 to facilitate the switch over to the new plant.

The first run-of-mine (RoM) material will be processed through the new plant in May 2017 using the existing dense-medium separation plant and final recovery sections.

The remainder of the new plant sections – the second mill, high-pressure grinding rolls, large-diamond-recovery and new final recovery sections – will be fully commissioned by the end of the fourth quarter of this year.

Any untreated RoM stockpile material at Cullinan will be processed in the first half of 2018, owing to the excess capacity of the new plant.

Key Contracts and Suppliers
MDM Engineering (front-end engineering design).

On Budget and on Time?
Unforeseen labour-related disruptions at the beginning of 2016, involving contractors at Cullinan, put some pressure on the commissioning schedule. This is expected to result in RoM tonnages treated for the first half of 2017 being between one-million and 1.5-million tonnes, compared with the earlier plan of 1.6-million tonnes, which included an estimated 350 000 RoM tonnes through the old plant for the period up to February 2017. RoM tonnes mined remain in line with expectations and any untreated material will be stockpiled. 

Contact Details for Project Information
Petra Diamonds, email info@petradiamonds.com.