The Carrapateena Project is located within the highly prospective Olympic Dam copper-gold (Cu-Au) Province. This is a metallogenic belt along the eastern margin of the Gawler Craton in South Australia, which hosts the Prominent Hill Mine, Olympic Dam mine and the Moonta-Wallaroo historic mining district. The Craton comprises variably deformed and metamorphosed sedimentary, volcanic and plutonic rock, spread from the late Archean to Mesoproterozoic, and it has been subdivided into a series of domains – the Carrapateena deposit being part of the Olympic Domain. The age of the iron oxide copper gold (IOCG) mineralisation in the Gawler Craton is uncertain, though it is interpreted in the literature to be associated with Mesoproterozoic magmatism of the Hiltaba Suite and the Gawler Range Volcanics.

The Carrapateena copper-gold mineral deposit is hosted in a brecciated granite complex, with both bornite and chalcopyrite copper mineralisation present – the bornite being a distinct higher grade zone of mineralisation.

The vast majority of copper and gold mineralisation within the deposit is hosted by hematite-dominated breccias with moderate mineralisation occurring within hematite altered granite breccias (Eastern Cu domain). Sulphides are the primary copper-bearing minerals in the Carrapateena Breccia Complex. Copper and gold mineralisation is structurally and chemically controlled, with subsequent alteration destroying mineralising structures. The most abundant sulphides are chalcopyrite, pyrite and bornite, and these constitute the majority of sulphides at Carrapateena. The less common sulphides are chalcocite, digenite and covellite, and in smaller amounts sphalerite and galena.

Gold mineralisation at the Carrapateena orebody is almost exclusively hosted by hematite altered breccias. Gold grains are usually very small (10 µm), and when seen in polished section, are often intimately associated with copper sulphides. Gold grains are commonly a combination of gold and minor silver (electrum).

The mining method chosen for the Carrapateena orebody is SLC ( sub-level cave).

The SLC design comprises the following lateral development components:
• Conveyor decline for conveying ore
• Decline adjacent to the orebody for level access – the Tjati Decline
• Total of 39 production levels, spaced at 25 m vertically
• First (or top) production level at 4585 m RL (approximately 485 mbs)
• Last (or bottom) production level at 3635 m RL (approximately 1,425 mbs)
• Crusher 1 located at 4530 m RL
• Crusher 2 located at 4205 m RL
• Crusher 3 located at 3855 m RL
• Main workshop, refuelling bay, wash bay and crib room located at 4430 m RL.

Level access drives will be developed from the Tjati Decline every 25 m vertically. These drives will lead onto the perimeter drives for each level. The level access drives were designed at a nominal gradient of minus 1:50 from the decline to the level sump. From the level sump, all drives were designed at 1:50 up to ensure that the level will drain to the sump.

Perimeter drives were designed with a 5.5 m high by 5.5 m wide development profile to enable truck passage under forced ventilation conditions (with vent bag installed). Truck loading during establishment of the levels will occur at the junctions of the perimeter drives and the SLC access cross cuts, or at the fresh air accesses.

Perimeter drives will be developed to the return air connections to establish a primary airflow along the perimeter drive prior to commencing drawpoint drive development. Sumps, stockpiles, ore pass accesses, and vent connections will be developed concurrently with the perimeter drive, as will the slot drives at the perimeter of the cave footprint.

Diamond drilling is included in the base case to allow definition of the main orebody and develop satellite ore potential. Resource definition drilling near underground infrastructure locations and definition drilling for the initial production levels has been factored into the design and schedule.

A number of the stockpiles in the upper part of the Tjati Decline have been positioned in suitable locations for this diamond drilling to be conducted before the top level development has commenced. This additional information will feed into updated block models for the Carrapateena resource, as well as the development of production geology models for operational use.

Ongoing diamond drilling will be required during the life of the operation to improve the confidence of the resource in the lower portion of the orebody. Additional drilling from underground will also add to definition of the orebody extents, with underground horizontal holes building on the surface vertical hole database.

The current dual decline arrangement for mine access and materials handling has many advantages. Of those, the main advantage to the materials handling system is the position of the conveyor within the drive profile. The dual decline arrangement allows the conveyor to be in a separate drive to the mine traffic and mounted lower to the ground, significantly reducing rock fall risk and the complexity of conveyor maintenance.

The underground materials handling system will be delivered in three portions. Portion 1, comprising the system down to the top of the orebody, will be delivered as part of the pre production capital program. Portions 2 and 3 of the system down to the middle and base of the orebody respectively, will be developed under future sustaining capital.

The minerals processing plant is designed to treat of crushed ore to produce a copper-gold flotation concentrate. Ore is primary crushed underground to a product size P80 of 106 mm. The Project FS base case assumes a start-up 4 Mtpa throughput rate increasing to 4.25 Mtpa after ramp-up.

The mineralogy is predominantly chalcopyrite and bornite, with minor amounts of chalcopyrite-pyrite and dilution materials. It is anticipated that the proportion of chalcopyrite-dominant ore will reach a maximum of approximately 87% in 2027.

The minerals processing plant will include the following processing stages:
• Conveying, stockpiling and reclaiming of crushed underground ore
• Grinding in an SABC (SAG mill, ball mill and pebble crusher) in closed circuit with cyclones producing a grind size P80 of 75 µm
• Recovery in a rougher flotation and regrind circuit
• Concentrate upgrading and removal of uranium with a Jameson cell and three stages of mechanical cleaners
• Thickening and filtering of the concentrate
• Stockpiling of the filtered concentrate in the concentrate storage shed prior to placement in containers for storage and load-out
• Thickening of tailings in a Hi-rate thickener and pumping to the TSF.

Flotation tailings will be pumped into the 27 m diameter hi-rate thickener. The underflow, with a density of 60% to 65% w/w solids, will be pumped via duty/standby pumps to the tailings hopper, and pumped to the TSF via a duty multi stage set of tailings pumps. Provision for a future standby set of tailings pumps has been included.