Independence Group (IGO) and JV partner AngloGold Ashanti have announced that a prefeasibility study (PFS) into the development of an underground mine beneath the Boston Shaker pits at Tropicana has confirmed that underground mining is technically and financially viable.

Boston Shaker Open Pit, underground development and access link to Tropicana. Image source ©IGO

AngloGold Ashanti and IGO are now progressing a Feasibility Study (FS), completion of which, and a financial commitment to the Boston Shaker underground development, is expected in the second half of FY19.

The PFS has confirmed that the development of an underground mine at Boston Shaker is technically and financially viable within a nominal PFS level of accuracy of+/- 25 per cent. The capital cost is estimated at A$95 million which includes mining development, in real terms on a 100 per cent basis.

IGO’s Managing Director, Peter Bradford, believes that the PFS demonstrates the potential viability of underground mining beneath the Boston Shaker open pits that integrates with the existing open pit life-of-mine.

“Delivery of Boston Shaker underground will result in an improved grade and gold production profile from Tropicana from FY21,” said Mr Bradford.

“The Pre-Feasibility Study is one of a number of work programs implemented at Tropicana to add value. The results are extremely encouraging, and we look forward to completing the feasibility study and potentially starting another exciting chapter at Tropicana.”

The underground mine design targets a production rate of 1Mtpa of material grading 3.7g/t to produce in the order of 100,000oz per annum over a life-of-mine of up to seven years.

This mine life is subject to the conversion of the underground Inferred Resources into Indicated Resources which is currently being executed as part of the FS. The initial portal development is anticipated to start from within the completed Tropicana pit in mid-2019. Full production levels should be reached in 2021, with the last stopes currently scheduled to be mined in 2026.

Underground material will be blended with open pit ore and processed in the existing mill. Interfaces between the Boston Shaker underground mine and the open pit mining activities have been incorporated into the 2019 business plan.

The metallurgical testwork completed as part of the PFS indicates that the current processing circuit is suitable to treat the underground material. The current throughput rate of 8.1Mtpa will be maintained. Metallurgical recovery remains in the 88-90 per cent range with no adverse effect expected on reagent consumption and/or the processing cost.

All infrastructure requirements to establish an underground mine have been scoped as part of the PFS. This includes an expansion to the mine village, additional Emergency Response facilities, workshops, power transmission lines and additional power generation capacity, as well as ventilation requirements.

Source: www.igo.com.au