The primary deposit has been identified as an alkalic gold-copper porphyry system, roughly elliptical in shape at surface (450 metres long by 150 metres wide) and with a vertical pipe-like geometry that extends to at least 800 metres below the surface. The porphyry-style mineralisation is closely associated with a zone of K-feldspar alteration, the extent of which is marked by the Didipio ridge, which is approximately 400 metres long and rising steeply to about 100 metres above an area of river flats and undulating ground.

Chalcopyrite and gold, along with pyrite and magnetite, are the main metallic minerals in the deposit. Higher grade gold and copper mineralisation is closely associated with the Quan Porphyry and Bugoy Breccia, both of which are elongate in plan-view along the north-south trending, steeply north-east dipping Tatts Fault Zone.

Porphyry style gold-copper mineralisation has been recorded over a strike length of approximately 450 metres, a width of up to 150 metres, and to a vertical depth of greater than 800 metres. The tabular composite intrusive and associated alteration and mineralisation strike in a north west – south east direction and dip steeply (80 to 85 degrees) north east. Higher grade gold and copper mineralisation is closely associated with the Quan Porphyry and Bugoy Breccia, both of which elongate in plain view along the Tatts Fault Zone. This mineralisation is surrounded by stockwork mineralisation that extends as a steeply east-dipping ellipsoidal shaped body, 110 metres to 140 metres wide, from the surface to a depth of 650 metres. Below a depth of 650 metres, the mineralisation is more tightly constrained forming a carapace around the Bufu Syenite, with extensions of higher-grade mineralisation continuing southwards along discrete structures. Higher gold-copper grades are also localised within the footwall (west) skarn, which is 5 metres to 15 metres wide, sub-vertical, open at depth and contains vein-type mineralisation over a strike length of 150 metres.

The deposit is oxidised from the surface to a depth of between 15 metres and 60 metres, averaging 30 metres. The oxide zone forms a blanket over the top of the deposit. A 5 metre to 15 metre thick transition zone is present over most of the deposit.

Brecciation of the QFC at the top of the Leached Zone (Bugoy Breccia) is characterised by high gold-copper grades. The gold and copper may have been remobilised and concentrated within the breccia matrix. Within the QFC Zone, highest grade mineralisation is generally coincident with an overlap of Mixed Zone alteration.

Grades are typically low where the Mixed Zone does not coincide with the QFC Zone at depth. The Mixed Zone is also notable in that it includes significant disseminated chalcopyrite-bornite- pyrite mineralisation, a feature not common in other alteration zones. Very high-grade gold-copper mineralisation is also a feature of the Skarn Zone where it occurs typically as coarse (2 mm to 4 mm) disseminations of chalcopyrite- bornitemagnetite overprinting the calc-silicate matrix. Outside the QFC Zone, chalcopyrite and gold mineralisation are generally lower-grade. Minor disseminated chalcopyrite may also occur with magnetite and chlorite as retrograde alteration of mafic grains. Locally, there is strong development of disseminated mineralisation.

The Didipio open pit mine was completed to final design in May 2017 after five years of mining. The underground project commenced in March 2015 with the construction of the underground portal and has continued development since. As of the end of year 2020 a total of 19,685 metres lateral development has been completed from commencement of project. This includes about 3.534 km of decline development, as well as other capital and ore drive development. The underground mine, along with processing of stockpiled open pit ore, is planned to be completed in year 2032.

Open Pit Mining
During the second quarter of 2019, mining took place at the base of the completed pit in order to extract a portion of ore in the crown pillar (2460 m RL to 2425 m RL) as part of the Crown Stabilisation Project (CSP). Once operations resume, the CSP project work will be completed. These works will establish a flat floor to the pit bottom. The ore mined from the crown pillar will be replaced with cemented rock fill to improve geotechnical stability, reduce the risk of water ingress to stopes during underground mining, and unlock further ore reserves in the Crown pillar which will be extracted from underground.

The rest of the crown pillar is planned to be mined once a suitable and geotechnically-sound method of extraction has been finalised

Underground Mining
Production from the underground mine is planned to ramp-up to 1.6mt of ore per annum.

The current underground mine design and plan is mostly based on the 2014 Didipio Technical Report, with a small modification to the mining method. On the Eastern side of the mine, the mining method has been changed from a combination of double-lift top-down and double-lift bottom-up longhole stoping to a strictly double-lift top-down approach. This is the result of learnings from the longhole stopes mined to date. The Western side of the mine remains a top-down approach.

Open pit mining and CRF backfilling, as part of the Crown Stabilisation Project, has enabled earlier extraction of the Crown Pillar reserves than previously planned.

Ore processing utilizes a conventional SAG and Ball mill grinding circuit and a secondary pebble crusher circuit.

Primary Crushing
The crushing circuit is situated next to the ROM pad. Mining trucks haul ore from the open pit to the ROM pad. ROM ore is fed by a front end loader (“FEL”) through an 800mm square aperture static grizzly into a 100-tonne live capacity ROM bin. The FEL is required to remove oversize material retained by the static grizzly.

The ROM ore is reclaimed from the ROM bin by an apron feeder and is discharged on to a static grizzly into a single toggle crusher. Fines will bypass the crusher. Static grizzly bars are set at nominally 100mm clearance.

The single toggle crusher, selected to handle 900mm maximum lump size, crushes the ROM ore to a typical P80 product size of 100mm. An overhead travelling crane is provided for changing out crusher jaw plates and for maintenance on other adjacent equipment. Dust suppression water sprays are provided at the ROM bin and at the head of the transfer bin feed conveyor, emergency stockpile feed conveyor and SAG mill feed conveyor. The sprays will be automatically turned on/off from the plant control system.

Primary and Secondary Grinding
The 7.3m diameter by 4.57m effective grinding length (“EGL”) grate discharge SAG mill is fitted with steel liners and pulp discharges and initially processed 2.5 Mtpa of ore. The SAG mill is equipped with a 4,300 kW wound rotor induction motor and Liquid Resistance Starter (“LRS”) and has capability to provide speed variation through a Slip Energy Recovery (“SER”) unit.

Media charging is from 900kg drums of 125mm grinding balls via a kibble to the mill feed chute. A target ball charge of 12% is maintained with a media addition rate of 0.28kg/tonne of feed. Mill load is determined from monitoring the hydrostatic pressure in the trunnion mill lube system and controls the mill feed rate. A microphone is used to monitor the mill for low load conditions to allow the mill speed to be reduced to minimise liner damage.

Discharge from the SAG mill flows through a rubber-lined trommel and into a common mill discharge hopper. Oversize from the trommel screen (scats) is directed to the scats recycle conveyor for return on to the SAG mill feed conveyor. A Sandvik CH-440 pebble crusher will be commissioned in Q4 2014 to reduce the scats size to -12mm. The current scats recycle conveyor discharge will be redirected into the crusher feed bin and a new transfer conveyor will transfer the crushed material back to the mill feed conveyor allowing the current system to be used as a crusher bypass.

The 5.5m diameter by 8.38m EGL rubber lined ball mill is fitted with a 4,300 kW wound rotor induction motor, LRS, trommel screen and retractable feed spout/chute. Discharge from the ball mill flows through a rubber-lined trommel into the common mill discharge hopper. The combined SAG and ball mill discharge is pumped to a nest of eight Krebs 20” hydrocyclones. The hydrocyclone underflow is split, with approximately 40% reporting to ball mill feed. The other 60% reports to an Outotec SK-500 Flash Flotation Rougher cell for recovery of the coarse liberated gold and copper particles. The concentrate from the Flash Flotation Rougher reports to a gravity circuit and the hydrocyclone overflow gravitates on to the flotation rougher circuit.

Ore processing utilizes a conventional SAG and Ball mill grinding circuit and a secondary pebble crusher circuit, followed by froth flotation for recovery of gold/copper concentrate. Flotation feed particle size is a nominal 80% passing 140um and milling capacity of 4-4.3MTPA though currently capped at 3.5MTPA under the ECC for the Didipio Mine. A gravity circuit is incorporated within the grinding circuit to produce gold bullion on site which accounts for 27-30% of total gold recovered.

The recovery for copper sits at around 91% when processing a blend of fresh UG & Stockpiled ore with higher recoveries to 94% on fresh ore alone. Overall Gold recovery ranges from 88 to 91%.

Gravity Circuit
The gravity circuit utilises a Falcon SB2500 concentrator batch concentrator. A bypass option allows the Flash Flotation Rougher concentrate to bypass the concentrator and report directly to the Flash Flotation Cleaner when the concentrator is in a rinse cycle or is offline. The other gravity circuit components consist of a surge bin for the concentrate, a Gemini table treating all the concentrate and a further Falcon model SB250 concentrator on the table tails, all of which is located in the secured area gold room.

The concentrate from the SB2500 concentrator unit gravitates to the gold room for further processing. The tailings from the concentrator reports to the Flash Flotation Cleaner TC-10 flotation cell where the coarse copper and gold particles are recovered with the concentrate, then report to the combined final concentrate hopper with the Re-cleaner concentrate and pumped to the concentrate thickener. The tailings from the Flash Flotation Cleaner report to a hopper and are then pumped back to the combined mills discharge hopper to be pumped back to the cyclones.

Flotation Circuit
Cyclone overflow reports by gravity line to the first of six rougher flotation cells. Outotec TC-40 tank cells are used for the roughers with progressively increasing froth crowders installed down the train. Rougher concentrates are pumped to the cleaner cells, the rougher tailings report to the flotation tailings hopper for pumping to the tailings thickener.

Concentrate from the cleaner cells feeds the bank of re-cleaner cells. Tailings from the re-cleaner cells re-join the rougher concentrate as feed to the cleaner cells. Concentrate from the re-cleaner cells will be directed to the final concentrate pumpbox and then transferred to the concentrate thickener. The tails from the cleaner cells feed into the cleaner-scavenger cells with the tailing from these cells reporting to the cleaner-scavenger cells. The tails from the cleaner-scavenger cells reports to the flotation tails pumpbox.

The concentrate from the cleaner/cleaner-scavenger cleaner cells can be fed to either the feed of the re-cleaner cells or the cleaner cells dependent on concentrate grade. The concentrate from the cleaner- scavenger cells reports back to the feed of the cleaner cells.

Concentrate Handling
Final copper concentrate is thickened in a 12m diameter high rate thickener fitted with a van feedwell and deaeration tank. The underflow is pumped at about 60-70% solids to a 400m3 storage tank. A Outotec PF-930 horizontal plate pressure filter press produces a concentrate filter cake at about 8% moisture, which will be suitable for transport and sea freight to smelter customers.