Mill Operations

(Introduction)

Ok Tedi Mining Limited mines and treats a large copper porphyry/skarn ore body at Mt Fubilan in the far north of the Western Province of PNG. The copper concentrator utilises a conventional sulphide mineral recovery and concentration process to produce a copper concentrate which is sold and exported to smelters around the world.

The concentrator has two parallel ore processing units which are essentially identical. After the run of mine ore has been crushed to a size of 150mm, it is conveyed to the stockpiles at the concentrator.

The processing flow sheet comprises:

  • Primary grinding in a semi-autogenous grinding mill
  • Secondary grinding in ball mills, in closed circuit with hydrocyclones
  • Copper mineral flotation in a conventional roughing / scavenging / cleaning circuit, and also includes a regrind circuit
  • Iron sulphide mineral flotation, in a conventional roughing / cleaning flotation circuit, for the recovery of a pyrite concentrate from the copper flotation tailings to address environmental constraints
  • Riverine disposal of tailings
  • Storage of the pyrite concentrate in purpose built pits

Each grinding circuit consists of a 9.8m diameter by 4.3m long SAG mill powered by twin 3500kW motors, and two 5.0m diameter by 8.8m long ball mills powered by 3700kW motors. The ball mills are in a closed circuit with 650mm diameter hydrocyclones.

Copper mineral flotation starts in a twin bank of OK38 flotation cells for roughing and scavenging. There are 18 of the OK38 flotation cells for roughing, and 12 of OK38 flotation cells for scavenging.

The rougher concentrates reports to the high grade regrind circuit which produces final concentrate via an OK100TC flotation tank tell. There is a 3.0m diameter by 4.5m long regrind mill in the circuit, and a gravity concentration circuit utilizing a XD30 Knelson Concentrator for optimising the payment of gold from the flotation process. The scavenger concentrates go into a cleaning and recleaning flotation circuit, each of which consists of bank of Denver DR500 flotation cells and another 3.0m diameter by 4.5m long regrind mill.

The copper concentrates are thickened in two 40m Dorr-Oliver thickeners. The thickened concentrate is directed to two storage tanks, from where it flows by gravity toward the filtration, storage, and load-out facility at Kiunga, 156 km to the south. A pump station at the 59km location provides assistance to this gravity flow. The filtered concentrates are transported by barges to the cargo vessels for shipment to the smelters.

The copper tailings are processed to remove most of the sulphide minerals from the tailings before they are disposed of to the riverine tailings system. These sulphide minerals are recovered using a conventional pyrite flotation process, in a series of OK150, OK200, and OK50 Tank Cells. This is an open circuit roughing and cleaning process.

The pyrite concentrates are thickened in a 40m diameter Envirotech thickener. The thickened concentrates are stored in two of 3000m3 capacity agitated storage tanks. The thickened concentrate is transported to Bige through a 250mm diameter pipe line. A Wirth piston diaphragm pump is installed at the head of the pipeline to ensure that the flow-rate is kept within the design parameters.

The tailings from the pyrite flotation process are thickened in two 50m diameter Dorr Oliver thickeners and the thickened tailings are discharged to the riverine tailings disposal system. Water is recovered from the concentrates and tailings thickeners for use as process water. Fresh water is used to make up the requirements of the process, and this is pumped up from the Yuk Creek System through three pump stations which are connected in series.

Limestone is mined from a quarry located near the concentrator. The limestone is burnt in two vertical kilns, which is then slaked to use for pH modification for the flotation and pipeline processes. The kilns are fired on a 4:1 mixture of waste oil and diesel fuel.

Production and Manpower

The concentrator can treat in excess of 22 million tonnes of ore per annum, to produce approximately 100,000 tonnes of copper, and 320,000 ounces of gold.

There are approximately 205 staff in the Concentrator Operations, Process Maintenance, and Process Technical Services departments (excludes Kiunga). The concentrator is manned and operated on a 24/7 basis, by three crews that work a rotating shift roster. There is a skeleton crew of maintenance tradesmen and assistants that also work the continuous panel roster. The rest of the maintenance and operations staff work twelve hours a day on their respective roster cycle.