The Higginsville mine is an underground and open-pit gold operation 150 kilometres south of Kalgoorlie, in the eastern goldfields region of WA.
Processing at Higginsville is by gravity and carbon-in-leach methods, and the mine produced 166,000 ounces of gold in 2010.
In August 2011 Alacer Gold announced an updated mineral resource estimate for Higginsville. The measured and indicated resource had increased by 10 per cent to 1.33 million ounces (inclusive of reserves).
In July 2010 Higginsville had proven and probable reserves of 5.7Mt grading 3.9 grams per tonne for 711,000oz of gold.
Alacer acquired the Higginsville gold operation as part of its merger with Avoca Resources in early 2011. Avoca discovered the Trident gold deposit, which contains the bulk of the reserves at Higginsville, in 2004, and mining of the deposit began in 2007.
The mine is situated between the prolific St Ives and Norseman gold camps. The Higginsville gold operation is made up of structurally controlled orogenic gold deposits occurring in the Archaean Norseman-Wiluna Greenstone belt, part of the Yilgarn Craton. Many of these deposits have been mined at surface, but aside from the Trident gold deposit, few have been explored extensively at depth. Alacer expected that with continued, aggressive exploration at depth, the future of Higginsville would extend far beyond the current reserves.
The Higginsville processing plant, a standard crush, grind, gravity and carbon-in-leach circuit with a throughput capacity of 1.3Mtpa, currently treats ore from the Trident underground mine, and from the Vine open-pit mine at which ore production began during the second quarter of 2011. The nearby Chalice underground mine is progressing towards commencing ore production in late 2011.
The primary mining method at the Trident underground mine is underground mechanised, sub-level open stoping. Stopes are backfilled with paste to ensure maximum recovery of the ore without the need for pillars.
Operating. Production results for the July 2011 quarter reported 40,919oz of gold, representing a 13 per cent increase over the previous quarter. For the March 2011 quarter Alcacer had reported that quarterly production has been less than forecast 40,881oz, representing a 12 per cent shortfall in ounces. The lower than expected gold production was related directly to mine grade reconciliation associated with the final Western Zone Sub Level Open Stope, and to lower equipment availability in the later stages of the quarter restricted ore hoist from Trident.