Consolidating one of Australia's great mining jurisdictions
Background
The Rasp Mine is an operating silver-lead-zinc mine located in Broken Hill, NSW. The mine hosts a Mineral Resource estimate of 10.1Mt at 9.4% ZnEq (5.7% Zn, 3.2% Pb and 49g/t Ag) (Rasp MRE) reported in accordance with the 2012 Edition of the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC Code), with a plant capacity of 750,000 tonnes per annum. There are presently ~118 employees and contractors engaged at the Rasp Mine.
Geology
The ore deposits at Rasp Mine are hosted by a sequence of Proterozoic meta-sedimentary rocks. Current mining operations are primarily focused on the extraction of the Western Mineralisation (WM) and the original Main Lode mineralisation.
The WM extends from approximately 100m below the surface to a depth of near 900m, where the deposit terminates against the Globe Vauxhall Shear. Mineralisation identified below this structure is associated with the Centenary Deposit which still remains open at depth.
Processing
The Rasp concentrator is designed to process up to 750,000 dry metric tonnes per annum of silver-lead-zinc ore. A single stage jaw crusher and two stage grinding circuit are used to liberate the valuable minerals from the waste rock. These minerals are then separated from the waste using the traditional, sequential flotation process.
Two concentrates are produced - a lead-silver concentrate and a zinc concentrate. Tailings from the process are placed in the surface tailing storage facilities in the Blackwood’s Pit (TSF 2) and the Kintore Pit (TSF3).
The concentrates are thickened and then filtered. The filtered concentrate is discharged directly into sealed concentrate containers which are then trucked less than a kilometre to the Rasp rail siding. The lead concentrate is railed directly to the Port Pirie smelter (or can also be exported) and the zinc concentrate railed to the Port of Adelaide where it is unloaded and ultimately shipped to smelter facilities globally.
Mining
Mining operations are undertaken predominantly by an owner/operator workforce, with contractors being utilised to undertake specialised support services including fibrecrete and diamond drilling. Current mining rates are approximately 30,000t per month for a 100% trucking operation to the surface.
Mining involves development drives similar to a tunnel to access the orebody and ore is extracted by the excavation of large underground voids called stopes. Underground stoping production is dependent on the ore geometry and geotechnical parameters. Stope techniques employed at Rasp Mine include longhole open stoping, modified avoca, cut-and-fill and room-and-pillar. Approximately 60 stopes are extracted per annum with mining depth at approximately 500 metres below the surface.
Once the ore has been extracted, waste material from the mining operation is used to backfill these voids. Currently this is in the form of unconsolidated waste material (rockfill) with the aim to utilise the existing sandplant in the manufacture of hydraulic fill in the future.