The Ravenswood expansion project involves the transition of the existing underground operations at the Ravenswood project located in Queensland, Australia, into open-pit mining operation. Resolute Mining, through its subsidiary Carpentaria Gold, owns the Ravenswood project.
The expansion project will involve the development of three large open pits, namely Nolans East, Sarsfield, and Buck Reef West.
Estimated to cost £117m ($150m), the expansion project is expected to produce approximately 115,000 ounces (oz) of gold a year. The total production is anticipated to be 1.5 million ounces (Moz) of gold through its mine life of 13 years.
The current Mt Wright underground mining operations will be terminated by the end of 2019, while the proposed open-pit mines will extend the mine life to beyond 2032. The expansion is anticipated to generate approximately 100 new jobs in addition to the 280 existing positions.
First gold at the Ravenswood site was discovered in 1868, with alluvial and shallow reef mining taking place between 1868 and 1880. Underground mining operations were conducted from 1897 to 1914.
Carpentaria Gold began exploration activities at the mine in 1978 and subsequently mining activities in 1987. Resolute Mining gained ownership of the project in 2004 and conducted mining activities at the Mt. Wright underground deposit until 2016.
Resolute came up with a pioneering open-pit mining technique involving sub-level shrinkage with continuous fill reviving open-pit operations.
Geology and mineralisation
The Ravenswood gold mine lies 95km from Townsville and 65km from Charters Towers in Queensland, Australia. It is situated in Ravenswood Batholith in the north-east part of Australia.
The regional geology comprises gold deposits hosted by several diorites intrusive in Jessop’s Creek Tonalite Complex belonging to the Silurian to Devonian age.
The mineralisation at the Tonalite Complex is observed as sulphide quartz shear lodes and narrow high-grade veins in both the Sarsfield and Buck Reef West deposits. The Nolans, Nolans East and portions of the Sarsfield deposit contain large quartz-sulphide vein stockwork. The deposits are intruded by diorite, quartz diorite, and minor gabbro rocks.
As of 2018, the Ravenswood gold mine was estimated to contain reserves of 1.8 million ounces (Moz). The mineral resources were estimated to be 4.4Moz.
Mining and ore processing at the Ravenswood expansion project
Mining operations at the existing mine are currently undertaken at the Mt. Wright underground deposit, until the end of 2019. A further 540kt of ore is expected to be mined and processed.
The underground mining operations are currently performed by using sub-level shrinkage with continuous backfilling. Conventional open-pit mining, using trucks and excavators, will be performed in the open-pits.
The Ravenswood expansion project will include two stages of mining, with the first stage involving mining and processing of ore from the Buck Reef West deposit from July 2019 and the second stage involving mining from the Sarsfield deposit from 2025.
The processing plant at Nolans will be upgraded to 3.2 million tonnes per annum (Mtpa) by the first quarter of 2020 and further to 5Mtpa by 2024.
Ore processing will be performed using a three-stage crushing circuit, followed by semi-autogenous grinding (SAG) and ball milling.
The resultant product will be passed through the carbon-in-pulp (CIP) processing circuit for the leaching process and subsequently to the gravity circuit to recover free gold. The gold recovery rate of the processing circuit is expected to be 91%.
Infrastructure facilities for the proposed Ravenswood expansion project
The Ravenswood gold mine property is accessible by road from the nearby town of Charters Towers, which is roughly 90km away.
Existing infrastructure facilities, including grid power, sub-potable process water, and transportation facilities, will support the proposed open-pit mining operations at the Ravenswood expansion project.