ALUMBRERA

PROCESSING

Marketing

The processing plant uses a conventional porphyry copper flotation circuit with proven, large scale equipment. MAL decided in 2001 to install a third grinding line and a pebble crushing circuit in order to meet the objective of maintaining concentrate production at lower ore grades over the life-of-mine.  MAL has increased the capacity of the rougher flotation circuit which was successfully commissioned in 2004 and is now operating at design levels.  During 2005, approval was obtained for the construction and installation of an additional Ball Mill which is scheduled to be commissioned towards the end of 2006 and will increase capacity.

In 2003 an expansion of the processing facilities was commissioned which increased throughput capacity to an average of 100,000 tonnes per day. The expansion facilities comprised an additional grinding circuit and a ‘pebble’ crushing circuit. The addition of a third grinding line helped maintain metal production as the ore grade decreased.

Mined ore is crushed in a gyratory crusher before being conveyed 1.7 kilometres to an 80,000 tonne live capacity stockpile.  Ore is drawn from the stockpile by apron feeders to conveyors feeding three parallel grinding circuits. The two original grinding lines each consist of a SAG mill and two ball mills operating in closed circuit with hydrocyclones. The third grinding line was added later and consists of a SAG mill and ball mill, both of which are reconditioned units.

An additional circuit was added in 2003 to crush stockpiled oversize ‘pebbles’ which are removed from the SAG mill discharge when processing harder ores with lower throughput rates. The crushed pebbles are conveyed via a surge bin to each of the three SAG mill feed conveyors.

SAG and ball mill discharge is pumped to a cluster of hydrocyclones with a minor proportion diverted via two centrifugal gravity concentrators for removal of coarser free gold. After conditioning with reagents, it is passed to the flotation circuit consisting of 32 mechanical flotation cells.

Some of the gold in the Alumbrera deposit is ‘free gold’, not finely encapsulated in other minerals, but freely liberated as discrete gold particles. The particles are very small, averaging about 10 microns, but a significant fraction of the gold can be separated from the other material by gravity processes.

The high density of gold allows a centrifuge-type device (called a Knelson concentrator) to separate the gold from other particles of lower density. The Knelson concentrate, which contains about 500 grams per tonne of gold, is transferred to the gold room for further upgrading to Dore bullion.

The plant produces two products, a copper flotation concentrate containing the major gold credit and Dore bullion from gravity recovery of coarser free gold.

The copper and gold concentrates are pumped with added water through a 316 km, 175 mm diameter pipeline over the Nevados del Aconquija Mountains to the province of Tucuman, where they are dewatered to obtain an almost dry product (7% moisture content).

From Tucuman, the concentrates are railed through the Nuevo Central Argentino (NCA) railway, with Alumbrera’s privately owned trains and covered wagons, to Alumbrera’s port facility in Puerto General San Martin, located near Rosario in the province of Santa Fe. The concentrate is loaded onto international vessels and shipped to overseas markets.

Process Flow Sheet

Marketing

Alumbrera has traditionally sold about 90% of its concentrate through frame contracts, with the balance being sold into the spot market. This has reduced the annual average treatment and refining charges and provided short-term flexibility for production, sales and revenue.

However, with the recent reduction in treatment and refining rates, Alumbrera’s strategy has changed to one of fulfilling the requirements of the frame contracts while directing any non-committed production to spot sales. In this way, the project is able to utilize the market conditions to their optimum advantage.

Alumbrera’s concentrate is shipped to smelters in Europe, India, the Far East, Canada and Brazil for refining into various copper products.

Substantial project infrastructure at Alumbrera

Infrastructure at Alumbrera