Audrey’s Mobrun project has initial recovery problem

Recovery problems have cropped up at the Mobrun project, shared equa lly by partners Audrey Resources and Corporation Falconbridge Copper. Located near Rouyn, Que., the deposit is being mined via open pit.

Audrey, which acquired a 50% stake after spending $5 million on the property, is shipping ore to Falconbridge’s Norbec mill. Although grades of the ore treated in the mill are similar to drill determined grades, recoveries of gold and zinc have been below estimates.

Zinc recoveries have averaged 61.6%, which is below the pilot plant average of 85%. Gold recoveries averaged 35.6%, which is below the average pilot plant recovery of 50%, Audrey reports. Copper and silver recoveries have been satisfactory.

As a result, net smelter returns for the first 27,000 tonnes of material milled at Norbec in October have been below forecast levels. The average return was $26.65 per tonne. Audrey has targeted a return of $35 per tonne from the open pit and $52.80 from the underground operation. Audrey President Guy Hebert, tells The Northern Miner that the low smelter return was due to low grade material required to tune up the mill. Returns in November are averaging $33-$34 per tonne he adds. Despite the lower return in October, Audrey actually made an operating profit of $5 per tonne, Mr Hebert says.

Audrey blames excessive oxidation of the ore in the first open pit bench for the low recoveries. Underground ore, which tends to be higher grading, is not as strongly oxidized which should improve zinc and gold recoveries, the company says.

Underground reserves total one million tonnes grading 0.84% copper, 3.59% zinc, 36.11 g silver and 3.12 g gold per tonne (0.09 oz gold per ton). The underground program, which will cost $8 million, is expected to be completed by March, 1987. By April, the mill feed will come from the underground mine. Financing for the work is in place.

For the 6-month period ended Sept 30, Audrey realized income of $2.3 million — generated by management, rental and interest revenues. An income surplus of $683,950 has been added to deferred expenditures.

The bulk sampling program, which began on Oct 1, is expected to improve the company’s financial performance during the third quarter.