The Boston Shaker underground project is a new underground mine being developed within the Tropicana gold mine in Western Australia.
AngloGold Ashanti Australia and Independence Group own the Tropicana project in a 70-30 joint venture.
Pre-feasibility study (PFS) for the underground mine was completed in December 2018. The deposit is being developed with an estimated investment of A$105.7m (£57m). It is expected to produce 100,000 ounces (oz) of gold a year over its mine life of eight years.
Construction on the project is expected to be commenced by the end of 2019. The first stope is anticipated to be mined in August 2020. The project is expected to start producing gold in the September quarter of 2020.
Boston Shaker underground project background
The potential viability of underground mining of the Boston Shaker pit at Tropicana mine was established in 2018. The gold production from Tropicana mine is expected to increase from 2021, following the commissioning of the Boston Shaker underground ore.
The Boston Shaker underground mine is expected to increase the mine life of Tropicana by one year, up to 2029.
Tropicana gold production is anticipated to be maintained between 450,000 and 500,000 ounces a year over five years, following the start of ore mining at Boston Shaker.
Boston Shaker underground project location, geology, and mineralisation
The Boston Shaker underground project, within the Tropicana Project, is located 330km to the east-north east of the city of Kalgoorlie in the Goldfields-Esperance region of Western Australia.
It is situated on the western margin of 700km-long magnetic feature, which is similar to the collision suture zone between Yilgarn Craton and the Albany-Fraser Origan.
The gold mineralisation at Tropicana is hosted by a shallowly south-west dipping sequence of quartz-feldspar gneiss, granulite, and meta-sedimentary chert lithologies.
Most of the mineralisation is made up of pyrite disseminations, bands, and crackle veins placed within altered quartzfeldspar gneiss.
The probable ore reserves at Boston Shaker underground project are estimated to be 2.8 million tonnes (Mt) grading 3.84 grams per tonne (g/t). The contained gold is estimated to be 317,000oz.
Mining and ore processing at Boston Shaker underground project
Mechanised mining and underhand sublevel open stoping method will be used at the Boston Shaker gold project. The method involves the blasting of 7.5m benches. The average mining rate is anticipated to be approximately 1.1 million tons per annum (Mtpa), to produce a total of 732,000oz.
The underground mine is proposed to be accessed through a decline within a portal underneath the Tropicana open-pit, while a second portal is proposed to be established in the completed Boston Shaker open-pit.
Major equipment proposed for the project includes two production drills, two jumbos, three remote capable loaders, and four trucks. The decline development will commence with the mining of the first stope at the portal, which is a part of the completed Tropicana mine.
The processing plant at the Tropicana mine will be used to process the ore produced at Boston Shaker project.
Underground material will be blended with the open-pit ore and processed in the existing mill. The ore at the Boston project will be processed at the Tropicana processing plant, which has a throughput rate of 8.1Mtpa.
At the processing plant, the ore will undergo two-stage crushing, followed by grinding in two ball mills and gold extraction in a standard carbon-in-leach (CIL) circuit. The resultant product will be subject to electro-winning to produce gold bars.
AngloGold Ashanti Australia awarded the Boston Shaker underground mine development contract to MacMahon Holdings in March 2019.