Long Island JV on track

AngloGold Ashanti Australia (AGAA) has announce that the partners in the Tropicana Joint Venture have approved Phase One of the Long Island strategy, increasing production from the mine in the medium term and extending mine life.

Long Island has been driven by developing a more cost-effective way to mine waste. It involves using a strip-mining approach that minimizes waste haulage distances by using in-pit backfill, rather than trucking the material long distances to surface waste dumps. The Tropicana Gold Mine, located 330km east-northeast of Kalgoorlie in Western Australia, is owned by AGAA (70% and manager) and Independence Group NL (30%).

Image credit: AngloGold Ashanti

Phase One of Long Island comprises mining of the Havana South pit and a cutback of the Boston Shaker pit, which uses the completed Tropicana pit as the first backfill location. The full Long Island strategy adds 2.1 million ounces to Tropicana’s business plan, extending mine life by about seven years to 2027.

The project value is enhanced by the decision to install a 6MW ball mill in the processing plant, enabling throughput to be matched to the increased mining rate and improving gold recovery by 3% to about 92%. Grade streaming, which prioritizes the processing of higher-grade ore and stockpiling lower-grade material for processing later, has resumed at Tropicana and will continue through 2018 and 2019.

Gold production (100%) is forecast to be between 478 000oz and 492 000oz next year and between 530 000oz and 548 000oz in 2019.

“This project is in line with our approach of developing cost-effective brownfield projects with attractive payback periods that extend life and improve margins,” says Michael Erickson, AngloGold Ashanti’s senior vice president Australia. “The project validates the innovative ideas developed by our site team and technical specialists, and gives us an excellent base from which we can investigate adding additional value through underground mining opportunities and regional exploration.”

Gold production over Tropicana’s remaining life of mine is now forecast to be about 4Moz. This does not include potential future underground production from mineraliasation at the Boston Shaker ore body, which remains open at depth. A pre-feasibility study on underground mining will be commissioned in 2018.

The Long Island strategy is underpinned by continued exploration success, evidenced by another increase in the Ore Reserve to 66.59Mt grading 1.91g/t for a total of 4.08Moz. This represents an increase of 280 000oz over the past year, even after depletion of about 550 000oz is considered.

Including gold produced to date, Tropicana has delivered a 72% increase in ore reserves since the Tropicana project was approved in November 2010.

Long Island strategy

As part of the cost-effective strip mining approach, waste haulage distances are reduced by using in-pit backfill. After initially considering mining a starter pit at Havana South to act as a void for waste in the proposed pit cutbacks, it became apparent from drilling that because there was limited upside beneath the Tropicana pit, it would provide significant value as a backfill location.

Mining rates at Tropicana have been successfully increased over the past year to more than 90Mtpa with the addition last year of a 600t face shovel, de-risking the increase to the Long Island mining rate of between 95 to 107Mtpa. The mining rate will peak at 107Mtpa in 2019 and continue at that rate for about four years until the bulk of the Havana pit is mined.

To achieve the additional material movement increase, a second 600t shovel with up to five additional Caterpillar 793 trucks and supporting ancillary equipment, will be added to the fleet. The capital expenditure related to Long Island will be about AUD18-million, primarily for expansion to the accommodation camp and heavy vehicle workshop infrastructure.

The additional fleet will be provided by Macmahon Holdings as part of the mining contract at the site. Productivity improvements through AGA’s Operational Excellence programme have resulted in a reduction in mining costs at Tropicana over the past two years to AUD3.07/t using conventional mining methods. It is anticipated that ongoing mining efficiencies will further reduce mining costs by 5 to 10% during Phase One.

Evaluation of open pit grade control drilling shows strong grade continuity in the Boston Shaker southern ore shoot. This, combined with the thick zones of high-grade mineralisation identified in recent exploration drilling, suggests the Boston Shaker ore zones will be amenable to underground mining.

A pre-feasibility study will be carried out in 2018 to investigate potential for underground mining at Boston Shaker with the aim of defining an underground ore reserve by the end of the calendar year. The PFS will include infill drilling and mining studies. Successful development of an underground mine at Boston Shaker has the potential to contribute high grade ore to the processing plant from 2021 onwards.

Click here for detailed information on Long Island


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