ALUMBRERA

THE FUTURE

MAA increased the capacity of the original plant to approximately 100,000 tonnes per day by the addition of the third grinding circuit, albeit using smaller equipment than that already installed.  The expansion also included a pebble crushing circuit to handle critical size material from the semi-autogenous grinding (“SAG”) mills, of which about 1 to 1.5 million tonnes, at 0.4% copper, already had been accumulated.   

MAA identified that the ball mill capacity was the limiting factor to additional throughput in the expanded plant and that a low capital option to increase throughput by approximately 10% to 110,000 tonnes per day (HOMt/a) was the installation of an additional 6.1 metre diameter, 9.34 metre long ball mill.

The project design includes a modification of the cyclone feed flow to grinding lines 1 and 2.  By extracting a portion of the cyclone feed flow and redirecting it to the new ball mill, extra capacity is achieved in lines 1 and 2.  This will optimize the operation by reducing the recirculation of pulp into the existing ball mills, increasing throughput and achieving a lower average grind size.  This circuit will no longer be the bottle-neck, resulting in an increase in SAG mill throughput.

The new mill configuration will have the flexibility to operate with a variable number of cyclones in each battery diverting flow to the new circuit and directing the crushed pebbles flow to SAG 1, 2, 3, or new ball mill.  This will allow the plant to operate more efficiently under any plant restriction, whether the restriction is in the SAG or ball mills.  It is anticipated that commissioning of this extension to the circuit will occur in the last quarter of 2006.

Although the cleaner flotation circuit is a constraint to feed metal, this will not be a problem except on the softest, high grade ore, as lower ore grade will compensate for the increased throughput.  MAA has not identified any other areas that require expansion, although it acknowledges that increased utilization in most areas is required.