Overview

Deposit type

• VMS

Summary:

The Rosebery volcanic-hosted massive sulphide (VHMS) deposit is hosted within the world-class Mt Read Volcanics. This Cambrian volcanic belt is an assemblage of lavas, volcaniclastics and sediments deposited in the Dundas Trough between the Proterozoic Rocky Cape Group and the Tyennan Block.

Mineralisation occurs as stacked stratabound massive to semi-massive base metal sulphide lenses. The host lithology lies between the Rosebery Thrust Fault and the Mt Black Thrust Fault which all dip approximately 45° east. Ore mineralogy consists predominantly of sphalerite, galena, chalcopyrite with electrum and minor tetrahedrite.

The orebody has experienced numerous events of folding, shearing and thrusting particularly in the late Cambrian and early Devonian. Lenses in the southern portions of the deposit have experienced metasomatism and replacement by a deep Devonian granitoid resulting in variation of the mineralogy, structure and alteration in these lenses.

Dimensions
The Rosebery Mineral Resource extends from -300mE to 1750mE, -800mN to 3325mN, 1650mRL to 3500mRL (Rosebery Mine Grid coordinates) and is currently open to the north, south and at depth.

Individual lenses vary in size from a few hundred metres up to 1,000m along strike and/or down-dip, with a total strike length of mineralisation reaching approximately 4,000m.

The mineralised lenses range from a minimum of 0.2-0.3m, maximum of 12-36m with an average true thickness of 3-6m.

Mining Methods

• Longhole open stoping
• Longitudinal retreat
• Transverse stoping

Summary:

Mining production is carried out by long-hole open stoping with decline access. Stoping is conducted through both longitudinal retreat and transverse methods.

Mining lenses are divided into panels and are mined using a bottom-up sequence with a number of levels being retreated simultaneously, either towards or away from level access drives. The nature of this mining sequence causes fluctuations in the grade profile in the short-term.

Backfilling of stope voids is carried out using two methods; cemented rock fill (CRF), and rock fill (RF). Up-hole (Crown) retreat stopes are left as open voids due to lack of access for fill placement. These open voids do not result in regional instability. The current mine closure plan identifies approximately 500kt of waste rock that has been stockpiled on the surface that is available for use as backfill when development material becomes insufficient to meet demands.

Average stope strike lengths of 15m were used in W and X Lens while the other lenses used 20m. The height set to 20-25m (floor to floor) and the minimum mining width of 4.5m.

Access to the orebody is through a decline 5.5m H x 5.5m W at a 1:7 gradient. The approximate horizontal standoff distance between the stoping footwall and major infrastructure; i.e. - stockpiles, vent rises, escape-ways and declines is 65-70m.

The current deepest production drive is approximately 1,700m below surface and the deepest economic drill intersection is approximately 2,000m below surface.

The primary ventilation system supplies approximately 660 m³/s (measured at depth) of air to the underground mine, which is sufficient to allow extraction from multiple ore lenses.

With all mining activity taking place underground at Rosebery, access to the operating areas is by the main decline, this route is used to access the upper-mid area of K Lens. From this point, access splits between two declines to the K/N/P Lens area and the W/X/Y Lenses. Other declines are used to direct primary airflow and for cross mine access. The ore is hauled out of the mine in a fleet of 45-60 tonne haul trucks.

Comminution

Crushers and Mills

Summary:

The Rosebery crushing circuit consists of a Primary Jaw Crusher and a Secondary Cone Crusher. During Crushing the ore size is reduced from around 650mm to P80 of 20mm. The Grinding Circuit consists of 2 x Primary Ball Mills and 3 x Secondary Ball Mills.

Processing

• Gravity separation
• Centrifugal concentrator
• Crush & Screen plant
• Smelting
• Flotation
• Concentrate leach
• Inline Leach Reactor (ILR)
• Dewatering
• Filter press
• Solvent Extraction & Electrowinning

Summary:

Rosebery is a poly-metallic underground mine with all ore processed through an onsite mill and concentrator. Metallurgical processing of ore from the Rosebery deposit involves crushing and grinding followed by flotation and filtration to produce saleable concentrates of zinc, lead and copper. In addition, doré bars are produced at site from partial recovery of gold and silver by a Knelson gravity concentrator.

The processing plant has a nameplate capacity of 1.0 Mtpa.

Traditional froth flotation has been used to float sulphur bearing minerals successfully for decades. The addition of a gravity gold recovery circuit allows for additional value to be recovered to the gold doré product. This is proven technology in the gold industry and has been operating successfully in this configuration at Rosebery for some time. The saleable products from this plant in its current configuration are doré, copper concentrate, zinc concentrate, and lead concentrate.

Gravity gold is recovered from the grinding circuits using 2x Knelson Concentrators. Gold Concentrates are leached in an Intensive Leach Reactor (ILR). Then recovered from the pregnant leach solution by electrowinning and thereafter the gold sludge is smelted.

The recovery sequence for sulphide minerals in the Flotation Circuit is Chalcopyrite (Cu), Galena (Pb), Sphalerite (Zn). Payable gold and silver is recovered with the copper and lead concentrates.

Concentrates are pumped to the Filter plant where they are filtered using Larox Filters. The filters produce a dry concentrate that is then transported via rail to Burnie.

Pipelines and Water Supply

Summary:

Rosebery’s fresh water comes from the Pieman and Stitt Rivers through a calibrated water balance model overseeing use and consumption. Risk management systems and site controls minimise stakeholder impacts within the catchment.

Production

Operational metrics

Personnel

Job Title	Name	Phone	Profile	Ref. Date
Electrical Superintendent	Shane Youd			Aug 9, 2024
Environmental & Community Manager	Adam Pandelis	(03) 6473 2221		Aug 9, 2024
General Manager	Steve Scott			Aug 9, 2024
Health, Safety & Security Manager	Wendy Hodgetts			Aug 9, 2024
Metallurgy Superintendent	Steve Pickford			Aug 9, 2024
Mining Manager	Andrew Flynn			Aug 9, 2024