Rosemont gold mine is a high-grade gold deposit located in Western Australia. The existing Rosemont open-pit is being expanded to underground in order to further exploit the contained gold.
Regis Resources is the owner and developer of the Rosemont gold deposit. Pre-feasibility study (PFS) of the underground project was completed in April 2019, which estimated a capital cost of £27m ($35.5m) for development. The mine life of the project is expected to be approximately five years.
The Rosemont project is expected to produce 230,000 ounces (oz) of gold. Its construction was started in February 2019 and first ore from development was achieved in the third quarter of 2019.
Rosemont underground gold mine location, geology, and mineralisation
The Rosemont gold mine is located within a distance of 10km from Garden Well gold project in Western Australia. It is situated approximately 100km to the north of the town of Laverton in the Goldfields Esperance region.
The gold occurrence is underneath the weathered profile in saprock and fresh rock. The upper saprolite is leached of gold.
The brittle fracturing and quartz albite sericite carbonate sulphide alteration within the quartz dolerite make up the mineralisation of the deposit. The mineralisation is north-northwest trending (NNW), occurs over a strike length of 4.9km, and inclines primarily to the west, while a few zones incline sharply towards the east.
Rosemont underground gold mine reserves
The proven and probable ore reserves at Rosemont underground gold mine are 0.6 million tons (Mt) of ore graded at 6.4g/t of gold. Contained gold is estimated to be 123,000oz.
Mining at Rosemont underground gold mine
The Rosemont underground gold mine will employ conventional trackless mechanised mining methods at its three zones namely Rosemont Main, Rosemont Central, and Rosemont South.
Rosemont Main zone will be extracted using long-hole open stoping method (LHOS) with back-fill, while ore from Rosemont Central and Rosemont South will be extracted using LHOS without back-fill.
The underground mine will be accessed through a decline from the existing open-pit, which will also help in fresh air intake. Primary exhaust adits are proposed to enter the open-pit in order to avoid vertical development through oxidised and transition zone material. The mined material will be conveyed to the surface by trucks.
Ore processing at Rosemont underground mine
The Rosemont underground mine ore will be treated using a process similar to that of the open-pit ore. The ore will be subject to crushing and grinding at the processing facility before being pumped to the nearby Garden Well carbon-in-leach (CIL) plant through slurry.
The average recovery at the Rosemont Underground Ore Reserve for Rosemont South and Central is estimated to be 94%. The Rosemont Main Zone is estimated to recover 92.5% of gold from the fresh open-pit ore.
The Rosemont underground gold mine will make use of the infrastructure existing at the open-pit mine, such as power, water, accommodation, and processing plant.
In addition, Regis proposes to construct underground pump stations, workshops, primary ventilation fans, and electrical infrastructure and expand explosive magazine and accommodation village for the underground mine.
Regis Resources engaged Entech for preparing the mineral resource estimate for the Rosemont underground mine.