The Cadia gold copper deposits are hosted by a late Ordovician to early Silurian volcano- intrusive complex which forms part of the larger zone of arc-related volcanic and associated intrusive rocks in the eastern Lachlan Fold Belt. Mineralisation at Cadia is hosted by the mid to late Ordovician Forest Reefs Volcanics and the underlying Weemalla Formation and by the late Ordovician to early Silurian Cadia Intrusive Complex. Postmineral cover comprises Silurian Cadia Coach Shale and a relatively thin capping of Tertiary basalts and gravels in some areas. Recognised structural controls include the regional northwest corridor – dilation zone thought to control the emplacement of the Cadia Intrusive Complex and post-mineral faulting in two dominant orientations striking northwest and north-south.

The Cadia East deposit is hosted within the Forest Reef Volcanics and porphyry intrusions. A north- east trending mass of narrow sheet like dykes of monzonitic to dioritic compositions intrude the lower parts of the Forest Reef Volcanics at Cadia East. These intrusives are largely restricted to the eastern half of the deposit although some narrow dykes and isolated bodies of monzonite have been recognised in the western end. At the upper western end of the deposit immediately underneath the Gibb fault, isolated narrow intersections have been identified with south dipping mineralised quartz veining. These occurrences are interpreted to be the Cadia Hill Monzonite.

Mineralisation at Cadia East can be divided into two broad overlapping zones: an upper, copper rich disseminated zone and a deeper gold-rich zone associated with sheeted veins. The upper zone forms a relatively small cap to the overall mineralised envelope and has a core of disseminated chalcopyrite, capped by chalcopyrite- pyrite mineralisation. The upper zone mineralisation is stratigraphically controlled within the volcaniclastic unit. This zone is transitional to the deeper vein style mineralization. The deeper zone is localised around a core of steeply dipping sheeted quartz- calcite-bornite-chalcopyrite-molybdenite, with the highest gold grades associated with the bornite- bearing veins. Copper and molybdenite form a mineralised blanket above and to the east of the higher grade gold envelope.

The geology model for the Cadia East deposit includes lithology, alteration, and structural faults. The structural interpretation includes the pyrite faults, Ca-La Crunch faults and Carbonate faults. Modelling of the fault planes and lithological boundaries comprises data obtained from drill core and underground mapping. The major faults were used as estimation domains, with semi- soft boundaries implemented where geostatistical testing warranted.

Cadia East is a large low to moderate grade, porphyry related gold and copper deposit that is located immediately east of Cadia Hill and separated by a major thrust fault (the Gibb Fault). Known mineralisation extends approximately 2.3 kilometres east-west, 1.1 kilometres north- south and 1.8 kilometres vertically. The deposit does not outcrop as it is overlain by between 80 and 200 metres of post mineralisation sandstones and shales. The mineralisation can be divided into two broad overlapping zones; an upper, copper- rich, disseminated zone and, a deeper gold-rich zone associated with sheeted veins.

The Study has re-assessed the orebody and determined an optimal mine design and operating sequence that is designed to be safe, resilient and which maintains production continuity as PC1 and PC2 are depleted and their production ramps down. The production profiles developed are constrained by the cave establishment sequence and the individual cave operational lifecycle.

The key findings and recommendations on mining from the Study are:
- The continuation of panel cave mining is the most efficient and economic mining method to extract maximum value from the Cadia East orebody and can be achieved in a safe and reliable manner;
- Long term productive capacity of the mine has been optimised; and
- an additional ~$540m will be required for the full development of PC2-3 following the gating of the Feasibility Study expected in the first half of FY20.

It is proposed that PC2-3 will use the El Teniente footprint layout with 32m x 20m drawbell spacing with 151 drawbells and a footprint of 97,000m2.

Processing of the Cadia East underground ore stream will be through Cadia Valley Operations Ore Treatment Plant concentrators 1 & 2. Metal recovery is through gravity and conventional flotation to a Copper/Gold concentrate. This circuit currently processes Cadia East Material with similarly styled material to future ore sources. Cadia East is the sole source of feed for both Concentrator 1 and Concentrator 2. Production of up to 33mtpa is anticipated to be produced through the concentrators. While the scale of processing will position the operation among the world’s largest gold mines, the technology associated with the ore processing is industry standard for this style of deposit and is already custom and practice at Cadia Valley Operations.

The process plant has already been progressively debottlenecked from 26mtpa, when Cadia East was commissioned, to the current rate of 30mtpa. The Study has identified further debottlenecking opportunities to increase the rate to 33mtpa and options to further debottleneck to 35Mtpa will be assessed during the Feasibility Study.

Concentrator 1 is currently constrained to 22mtpa by the SAG Mill. Projects to further debottleneck the SAG Mill have been identified which, as estimated in the Study, can potentially increase throughput by approximately 3mtpa to 25mtpa. Concentrator 2 has recently undergone a significant debottlenecking program that has increased annualised throughput from 6.5mtpa to 8mtpa. Incremental capital expenditure of $58M is required for upgrades to the underground materials handling system and the installation of additional crushing capability within the Concentrator 1 plant at Cadia.

The Study proposes the construction of a new secondary crushing circuit for the Concentrator 1 milling circuit including a crusher with a secondary screening feed, a pebble crusher and a 1.5 megawatt (MW) ball mill.

The advantages of the combined debottlenecking of Concentrator 1 milling circuit option include:

- Capital efficiency – as it requires lower capital expenditure
- Design and operational simplicity
- Ease of implementation.

The Study found that additional infrastructure is expected to increase the Concentrator 1 milling rates to 25mtpa. Recent upgrades to Concentrator 2 have increased its capacity to 8mtpa. The total surface milling rate is expected to be 33mtpa combined.