The Cadia Hill deposit is a sheeted quartz vein system located almost entirely within the quartz monzonite porphyry phase of the Cadia Intrusive Suite.

The predominant alteration is propylitic (chlorite-epidote) with narrow domains of structurally-controlled phyllic (sericitic) alteration. Mineralization is in part related to chlorite matrix hydrothermal breccias that cut the deposit. Unusually, compared to the other mineralized systems in the area, potassic alteration is confined to K-feldspar rich vein haloes and to some quartz veins.

The vein system forms a broad, 300 m wide tabular envelope that dips 60° to the southwest. Chalcopyrite with lesser bornite, pyrite and gold occur in the quartz veins and as disseminations throughout the intrusive wallrock.

A feasibility study on mining the Cadia Hill deposit was completed in 1996 with project funding approved in September that year. The feasibility study open pit design, which included a number of planned cutbacks.

Concentrator 1: • Primary crushing in a 60-inch x 113-inch gyratory crusher. This was the main primary crusher for the original Cadia concentrator and now primarily used for surface stockpile reclaim; • Coarse ore stockpile (COS) to a live capacity of 40,000 t and subsequent reclaim facilities; • Distribution bin and double-deck vibrating screens for feed size preparation; • Secondary crushing, treating screen oversize, using MP1000 cone crushers; • High pressure grinding rolls (HPGR) unit treating screen undersize prior to the SAG mill; • Primary open circuit milling in a single 40-ft SAG mill fitted with a 20 MW motor. The motor will be upgraded to 22 MW. Oversize pebbles from the SAG mill are returned to the distribution bin; • Secondary milling in three ball mills, with the two original mills fitted with 8.7 MW motors, and a more recently installed third ball mill with a 16 MW motor. The mills are in closed circuit with cyclone classification for a target grind size of P80 of 150–190 µm. Concentrator 2: • Reclaim and conveying system to transfer ore from Concentrator 1 COS to Concentrator 2 facilities; • Secondary and tertiary crushing using MP800 cone crushers and open circuit prescreening; • Dedicated coarse (crushed) ore stockpile (COS) and apron feeder reclaim facilities; • Primary open circuit milling in a single SAG mill fitted with a 7.5 MW motor; • Secondary milling using a 7.5 MW ball mill and parallel Vertimill VTM1250, in closed circuit with classifying cyclones. • Tertiary milling using a Vertimill VTM 3000. Cadia’s operating and financial performance in FY22 was impacted by reduced throughput rates during the planned replacement and upgrade of the SAG mill motor which commenced in early July 2021 and was successfully completed in November 2021, together with the expected decline in grade.

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