Overview

Deposit type

• Footwall hosted
• Breccia pipe / Stockwork
• Sediment-hosted

Summary:

The Dugald River style of mineralisation is a sedimentary and shear hosted base metal deposit. The main sulphides are sphalerite, pyrite, pyrrhotite and galena with minor arsenopyrite, chalcopyrite, tetrahedrite, pyrargyrite, marcasite and alabandite.

The deposit is located within a 3km-4km along strike north-south trending high strain domain named the Mount Roseby Corridor and is hosted by steeply dipping mid Proterozoic sediments of the Mary Kathleen Zone in the Eastern Succession of the Mount Isa Inlier. The host sequence is composed of the Knapdale Quartzite and the Mount Roseby Schist Group (which includes the Hangingwall calc-silicate unit, the Dugald River Slate and the Lady Clayre Dolomite). The sequence is an interbedded package of greenschist to amphibolite grade metamorphosed carbonate and siliclastic lithologies.

The main Dugald River lode is hosted within a major N-S striking steeply west dipping shear zone which cross cuts the strike of the Dugald River Slate stratigraphy at a low angle. All significant zinc-lead-silver mineralisation is restricted to the main lode. Lesser-mineralised hanging wall and footwall lenses are present.

The five main types of mineralisation style recognised at Dugald River are sulphide stringer, banded ore, slatey breccia, pyrrhotite-slatey breccia and massive breccia.

The geometry of the deposit consists of the boudinaged main lens, which pinches and swells in thickness along strike and to depth. It is recognised that the previously modelled hangingwall and footwall domains (1A, 2, 3, 4 and 5) are part of the main lens which anastomoses, splits and merges. All zinc and associated lead-silver mineralisation are governed by this geometry.

The mineralogy of the Dugald River lode is typical of a shale-hosted base metal deposit. The gangue within the lode is composed of quartz, muscovite, carbonates, K-Feldspar, clays, graphite, carbonaceous matter and minor amounts of calcite, albite, chlorite, rutile, barite, garnet, and fluorite.

The mineralised zone extends approximately 2.4km in strike length and up to 1.4km down-dip.

Dimensions
The Dugald River lode is hosted within a major N-S striking steeply west dipping shear zone which cross cuts the strike of the Dugald River Slate stratigraphy at a low angle.

The strike length of mineralisation is approximately 2,400 m. Dip varies between 85° and 40° to the west.

The true thickness of the majority of the Mineral Resource is between 3 m and 30 m with the thickest zones occurring to the south.

The mineralisation is open at depth. The deepest drill intersection of mineralised material is about 1,140 m below the surface.

Mining Methods

• Longitudinal open stoping
• Transverse open stoping
• Sub-level open stoping (SLOS)
• Longhole open stoping
• Avoca

Summary:

Mining at Dugald River is underground with the mining methods being Sub-Level Open Stopes (SLOS), both Longitudinal and Transverse, in the South Mine and Longitudinal with rib pillars in the North Mine. Level intervals occur every 25m and stopes have a strike length of 15m. Currently the deposit is accessed by two declines.

The orebody access is split into a north and south mine, due to its 2 km strike length and a low-grade zone at the extremities of the orebody.

The north mine is narrow (average ~5 m true width) and sub-vertical. The south mine is wider than the north mine with a flexural zone in the centre. The south mine is narrow and steep in the upper zone (~top 200 m from surface) and lower zone (~below 700 m from surface). The central zone is flatter and thicker than the upper and lower zones.

The stopes are broken into the following categories:
– Longitudinal SLOS, for stopes up to 10-15m wide horizontally. (Where the orebody has thickened adjacent stopes are mined in sequence after paste filling).
– Transverse SLOS, for stopes where the orebody thickness lends itself to sequential stope extraction retreating along cross-cuts.
– Crown pillar SLOS, for the top level of each panel where stoping occurs directly below a previously mined area.
– Longitudinal SLOS for the North Mine, where a rib pillar is also left.

The parameters used to create the stope shapes were:
– All Mineral Resources categories included;
– 25 m level interval;
– Variable strike length;
– Minimum mining width (MMW) of 2.5m;
– The minimum dip of 52 degrees for Footwall (FWL) and 37 degrees for Hanging wall (HW);
– Minimum waste pillar between parallel stopes of 7.5m; and
– A BcoV associated with the appropriate mine zone, applied to create initial stope shapes.

The underground (UG) mine is accessed via two separate declines and as such the mine is split into two – north and south, although both declines are connected via a link drive approximately every 150m vertically at the base of each production Panel. As of 30 June 2023, 9,867m of decline has been mined, along with a further 77,953m m of lateral development (excluding 5,201m of paste development). A third in-mine decline in the south mine, for independent access to Block A, has commenced, that included drill platforms for resource conversion.

Currently, six raise-bored ventilation shafts have connection to the surface:
– The southern Fresh Air Raise (FAR1) – at 3.5 m diameter and 90m depth;
– The southern Fresh Air Raise (FAR2) – at 5.0 m diameter and 190 m depth; with a120m and 130m extensions to the 340 level and 490 level respectively.
– The southern Return Air Raise (RAR1) – at 5.0 m diameter and 154 m depth; with a 375m extension (multiple holes) to the 565 level.
– The southern Return Air Raise (RAR2) – at 5.0 m diameter and 197 m depth; with a 270m extension (multiple holes) to the 490 level and a further 135m extension to 640 level.
– The northern Fresh Air Raise (FAR) at 3.5 m diameter and 165 m depth with a 275m extension (multiple holes) to the 490 level and a further 130m extension to the 640 level.
– The northern Return Air Raise (RAR) at 5.0 m diameter and 104 m depth with a 310m extension (multiple holes) to the 490 level and a further 140m extension to the 640 level.
– On each return shaft collar there is an exhaust fan drawing approximately 270-300m3/s.

There is also a secondary RAR system in the north and south mines comprising of LHW and 3.0-3.5m raise bored holes that have connections to each production level where there is access.

Secondary egress is provided by link drives between the South & North declines. These link drives are positioned at the base of each production Panel. The lowest connection to date has been made at the base of Panel 4 on the 640 Level.

An internal ladderway also exists in the South mine between the 50 and 200 Levels. In addition, strategically placed refuge chambers are to be found throughout both mines.

Comminution

Crushers and Mills

Summary:

The metallurgy process proposed for the Dugald River deposit involves crushing and grinding.

Processing

• Crush & Screen plant
• Flotation
• Dewatering

Summary:

The metallurgical process for treatment of Dugald River ore involves crushing, grinding followed by sequential carbon/lead/zinc flotation to produce separate lead and zinc concentrates. The carbon concentrate is a waste product and reports to final tailings. This process, and the equipment used, is conventional for this style of mineralisation and used worldwide.

The Dugald River processing facility was commissioned with production commencing in October 2017, with nameplate throughput reached after 7 months of operation(May 2018). Both lead and zinc concentrate produced at Dugald River meet saleable grade and impurity specifications.

Deleterious elements include manganese and carbon, which have been estimated in the block model. Manganese percentage in the zinc concentrate is calculated as a postprocessing step to allow the generation of a value that can be used for the Ore Reserves.

Water Supply

Summary:

Process Water Dam(PWD) water would need to be utilised to the maximum practicable extent in processing and related mine activities (e.g. dust sprays, mine service water streams). Additional water for the operation, including for potable water supply, would be sourced from Lake Julius due to a lack of significant local groundwater resources in the area.

Dugald River’s water management structures are appropriately designed to oversee the high intensity flow events of the wet season through defined catchment zones and dams while during the dry season an emphasis is placed on balancing water conservation and optimising reuse.

Production

Operational metrics

Personnel

Job Title	Name	Phone	Email	Profile	Ref. Date
Environmental Superintendent	Gemma Green	0434-870-089	gemma.green@mmg.com		May 14, 2024
HSE & Community Manager	Robert James				May 14, 2024
Maintenance & Engineering Manager	Norm Doxanakis				May 14, 2024
Maintenance Superintendent	Noel Irwin				May 14, 2024
Manager Underground Technology	Adam Barton				May 10, 2024
Processing Manager	Simon Fitzpatrick				May 14, 2024