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The Callie Underground Mine is located in the Tanami Desert 560 km Northwest of Alice Springs in the Northern Territory and is currently operated by Newmont Australia Limited with all mining activities carried out by Henry Walker Eltin. Callie was discovered in the region in 1991 with the box cut portal commenced south of the pit in 1995 and underground ore production commenced in 1998, after completion of the profitable Callie Open Pit. Ore production is approximately two million tonnes per annum from large sublevel open stopes. All ore is hauled to the surface by a fleet of seven 55 tonne diesel dump trucks via a one in eight decline from sublevel open stopes, with development waste dumped at underground tip points throughout the mine for stope backfill.

The climate is tropical continental with a distinct wet and dry season. During the wet season from September to March, average daily maximum dry bulb (DB) temperatures are between 33 degrees C (September) and 39 degrees C (December) Surface temperatures in excess of 40 degrees C dry DB are typically recorded more than 50 times a year with a daily maximum up to 47 degrees C dry bulb recorded.

Development is currently occurring at depths of over 700 in with the decline currently below the 640 Reduced Level (RL) level (surface RL of 1400) with production haulage from 600 in below the surface. The combination of auto compression, a moderate geothermal gradient of 2 degrees C/100 in and diesel heat transfer causes the wet bulb temperature of intake air at the bottom of the mine to be typically 5 degrees C higher than on the surface. Wet Bulb temperatures can be up 5 degrees C higher again in active areas under secondary ventilation.

During the 2002/2003 wet season many activities in the lower levels of the mine were stopped due to miners experiencing adverse heat related symptoms or the temperatures exceeding the Underground Heat Management Procedure stop job criteria of 32 degrees C wet bulb.

To improve the working environment, combat the heat related illness and improve operational efficiency, a temporary 1.8 MW refrigerated cooling plant consisting of three 600 kW modules were installed underground to provide bulk air cooling for the lower levels of the mine during the 2003/2004 wet season.

Several studies have been conducted in relation to future ventilation demands at Callie and all came to the conclusion, that some mine cooling will be necessary for Callie to meet the high production and development demands.

This paper will describe the ventilation network at the Callie Underground operation focusing on the installation, operation and effectiveness of the temporary underground refrigeration plant.