Overview

Deposit type

• Vein / narrow vein
• Porphyry
• Breccia pipe / Stockwork

Summary:

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.

Mineralisation
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 northwest – southeast 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, subvertical, 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-bornite-magnetite 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.

Mining Methods

• Longhole open stoping

Summary:

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. Top-down longhole open stoping with pastefill is used throughout the mine.

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 as part of the Crown Stabilization Project (CSP).

The underground mine, along with processing of stockpiled open pit ore, is planned to be completed in 2035 based on Mineral Reserves only.

Open Pit Mining Method
Large scale open pit mining is complete however a small amount of material remains as part of the CSP. The mining method for the removal of the CSP material via the open pit is conventional drill, blast, load and haul with standard mid-sized mining equipment comprising 90 tonne class off-road haul trucks and 200 tonne excavators.

In the first quarter 2022, the Company commenced and completed the strengthening of the crown pillar from surface. As a result, ore was sourced from both the surface and underground. Ore mined from the crown strengthening pillar totaled 176,867 tonnes and ore mined from the underground totaled 308,691 tonnes. The Company does not anticipate any further surface extraction until the end of the mine life when mining of the remaining crown pillar is planned.

Underground Mining
Current underground designs extend approximately 340m below the base of the open pit to the 2100mRL with the main decline face at 2180mRL.

A fleet of 17 tonne Load Haul Dump loaders (“LHD”) and 60 tonne trucks are used for material loading and transport from the underground working areas through an internal ramp system that connects all production levels to the main decline. Loading occurs in close proximity to the stoping areas and ore is hauled directly to the existing coarse ore stockpile (ROM) adjacent to the processing plant.

Since portal establishment in 2015, 20km of lateral development has been completed. Based on current Mineral Reserves, an additional 28km of lateral development is required for capital infrastructure and to access all stoping blocks, with a peak advance rate of 400m per month of jumbo advance. Vertical waste development related to ventilation infrastructure and emergency egress is mined via a combination of longhole drill and blast, and raisebore. Waste generated through lateral and vertical development is hauled directly to the bottom of the pit to be used for CRF, or to the surface waste dump later in the mine life. With paste fill utilised for backfill, no internal haulage and stockpiling of waste underground is required. Approximately 1.02Mt of waste will be generated over the remainder of the LoM.

Key mine infrastructure includes two 5.5m diameter exhaust ventilation raises with accompanying primary fans, a 5.5m diameter intake fresh air raise, and an underground ladderway system located within fresh air which provides a second means of egress to the surface via an additional portal located at 2540mRL in the southern wall of the pit. The paste backfill plant and associated infrastructure is located on the surface with underground reticulation to transfer paste to underground stopes. An underground dewatering system is currently in place, with the main pump station and water storage stope located at the 2250mRL Level. An additional pump station, wastewater storage stopes, and associated infrastructure is planned for the 2160mRL Level to provide additional dewatering capacity for the lower levels of the mine.

Mining Method
The LHOS mining method, is a commonly employed, high-production, low-cost mining method that is suited to steeply dipping tabular-like orebodies. The method allows a high degree of mechanisation and offers good mining selectivity, good recovery and is relatively flexible to suit variable geometries and ground conditions.

The LHOS mining method can provide a high production rate once sufficient stopes are accessed. The method is considered low risk because mining crews do not have to enter the stope void. Remote loading of blasted ore is required once the stope brow is open to the extent where the operator may be exposed to uncontrolled sloughing from the stope cavity. Line of sight loading is not utilised at Didipio - all remote loading is conducted either from tele-huts located underground or from the surface (generally utilised over shift change).

Production can commence from a stope once the top and/or bottom development ore drives (in ore) are established, and the expansion slot raise is mined between the two levels. Didipio have recently employed a Rhino raisebore rig to improve slot raise productivity and accuracy. The Rhino rig drills an initial 750mm diameter uphole before infill stripping holes around the raisebored hole are drilled with a production rig to create sufficient initial void. These infill stripping holes and all other production holes are drilled with a top hammer drill rig. Drilling is a combination of upholes and downholes. Once loading and hauling of blasted ore is complete, backfilling commences with the placement of paste backfill that will be re-exposed during the extraction of the next stope in sequence. Once sufficient curing time has been allowed, the slot drive is developed in the immediately adjacent stope and the extraction sequence can commence. A primary/secondary stoping sequence is utilised at Didipio, where primary stopes are separated by a secondary stope. Extraction of the secondary stope can only occur after the two immediately adjacent primary stopes have been mined, backfilled and have had time to cure.

The production front at Didipio is divided into two panels – Panels One and Two. Panel One comprises levels 2280mRL up to and including the crown pillar levels 2400mRL and 2430mRL. Panel Two comprises of levels 2100mRL up to 2250mRL. Previous iterations of the Didipio production sequence contained a sill pillar at the 2250mRL level and a predominantly bottom-up mining sequence.

Access and Mine Infrastructure
The main access decline was driven at a one in seven gradient for 4.0km from the surface portal and provides access for personnel and equipment. The decline has been sized at 5.8mW x 6.0mH to provide adequate clearance for mobile equipment operation, and to enable a low resistance intake air way. The main access decline face has advanced to the 2180mRL, leaving approximately 780m of lateral decline advance remaining to access the bottom three levels of the mine (2160mRL, 2130mRL and 2100mRL). The decline advance rates have been prioritised to ensure active dewatering and adequate pumping infrastructure is installed ahead of the advancing production front in the lower levels of the mine. An additional portal is also located lower down the pit wall which provides a second means of egress and additional fresh air supply.

The three initial ventilation shafts collared on the surface were raise bored at 5.5m diameter however as the mining levels are developed from the access decline and the primary ventilation network is extended incrementally, shafts in between levels are mined utilising longhole blasting (6m x 4m profile). A total of nine return air shafts and three fresh air shafts remain to be completed in the current LoM to deliver primary ventilation to the lower production levels. A ladderway escapeway system that extends to the surface via the secondary egress portal also extends incrementally between levels via 1.1m diameter raise bored holes. A combination of fully caged steel ladders, and fully enclosed plastic laddertube have been utilised within the escapeway network.

Level Development
Vertical sublevel spacing (floor to floor) is 30m which is defined by planned stoping heights. Decline stand-off from the footwall drive varies based on infrast

Comminution

Crushers and Mills

Summary:

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.

Processing

• Gravity separation
• Crush & Screen plant
• Centrifugal concentrator
• Shaker table
• Flotation
• Dewatering
• Filter press

Summary:

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 160 um and milling capacity of 4.0 Mtpa to 4.3 Mtpa. A gravity circuit is incorporated within the grinding circuit to produce gold bullion on site which accounts for 30% to 34% of total gold recovered after the completion of gravity circuit and gold room upgrade in July 2022.

Recovery of copper and gold at Didipio is achieved from the use of a combination of flotation following a conventional SAG mill/ball mill grinding circuit and gravity gold recovery. The design criteria for the process plant, was established from test work outlined in Section 13 of this report. The plant has been successfully running and exceeding 3.5Mtpa nameplate since the 2014 processing plant upgrade, with a well-established workforce and management team in place until June 2019 when operations were suspended. Following renegotiation of the FTAA in July 2021 the plant was restarted in November 2021 with full production expected in Q2 2022.

In the process flowsheet ore is processed using a conventional SAG/Ball mill/Pebble Crusher (SABC) grinding circuit with a secondary pebble crusher circuit followed by froth flotation for recovery of gold/copper concentrate. A gravity circuit is incorporated within the grinding and flotation circuits to produce gold bullion on site. Copper concentrate is transported by road to the San Fernando port facilities for export.

Gravity Circuit
The purpose of the gravity circuit is to recover free gold from the Flash Flotation concentrate. The gravity circuit utilises a Falcon SB2500 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. Other gravity circuit components consist of a surge bin for the concentrate, a Gemini and a Deister table treating all the concentrate and a further Falcon model SB250 concentrator on the table tails, all of which are located in the secured area of the 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.

An additional Falcon SB750 batch concentrator was installed in November 2016 in fine flotation circuit and was fully operational in February 2017. This gravity concentrator treats the Rougher concentrate stream prior to entering the Cleaner circuit. The concentrate from SB750 reports directly to the surge bin in the gold room while the tailing goes to the Cleaner circuit. A bypass option allows the Rougher concentrate to bypass the concentrator and report directly to the Cleaner circuit when the concentrator is in a rinse cycle or is offline.

Flotation Circuit
Cyclone overflow reports by a 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 Falcon SB750 fine gravity concentrator (GC003), while rougher tailings report to the flotation tailings hopper for pumping to the tailing’s thickener. Tails of the GC003 feed the cleaner bank, and its concentrate is discharged to the gold room.

Concentrate from the cleaner cells feeds the bank of re-cleaner cells. Tailings from the re-cleaner cells mix with the GC003 tails as feed to the cleaner cells. Concentrate from the re-cleaner cells is directed to the final concentrate pump box and then transferred to the concentrate thickener. The tails from the cleaner cells feed into the cleaner-scavenger cells, while the tails from the last cleaner-scavenger cell report to the cleaner tails hopper, and then pumped back to the rougher feed bank.

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

A control system called FrothSense was installed in 2016 to automatically control the operating parameters of the flotation cells.

Concentrate Handling
Final copper concentrate is thickened in a 12m diameter high-rate thickener fitted with a vane feed well and de-aeration tank. The underflow is pumped at about 60-70% solids to a pair of 450m3 storage tanks. 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. As part of the efforts to increase the annual throughput to 3.5Mtpa, four additional plates were installed in the concentrate filter to increase its capacity by 20%.

The filter cake discharges to a concentrate stockpile of about 15 days capacity located within the concentrate storage shed. The concentrate is loaded into dump trucks using a FEL with a nominal payload of 20 wet tonnes per load. Composite samples are prepared from trucks as they are loaded, for moisture and metal content. A weighbridge weighs all trucks leaving site to account for movement, inventory control of material and tracking for permit requirements.

Concentrate is trucked by road to a storage shed located at Poro Point, La Union with the capacity to hold up to 15,000t of material. Ships are loaded periodically in 5,500t or 11,000t shipments. Turnaround time for the concentrate trucks averages 27-32 hours.

Tailings Handling
Flotation tailings from the hopper are pumped to a 20m diameter high-rate thickener with a vane feed well. Flocculant, MAN 4510 and MNI 4520 are dosed to the thickener feed box by variable speed helical rotor pumps to aid in the settling of tails and to provide necessary clarity in thickener overflow.

Three stage variable speed thickener underflow pumps pump thickened tails to the Tailing Storage Facility (TSF) through a 250mm steel/HDPE line approximately 2,000m to the dam crest. Tailings then moves through a spigot manifold along the length of the dam wall allowing formation and control of the tailings beach. Approximately 340m3 /h of decant water (a mixture of tailings transport water and rainfall in the catchment) is pumped back to the process plant for makeup water. Excess water in the catchment is pumped to the water treatment plant for release.

Approximately 40-50% of tailings from the process plant are fed to the paste back-fill plant.

Gravity Gold Concentrate Treatment
The concentrates from the Falcon SB2500 and Falcon SB750 concentrators are screened with a Amkco Vibrascreen. The screen oversize product reports to the Gemini shaking table while the undersize product is treated using the Deister shaking table. Concentrates from the tables are filtered and dried prior to smelting in a standard diesel-fired barring furnace. The tailings and middling’s product from both tables are retreated in a small Falcon concentrator, with the concentrate joining the Deister feed. The tailings from the Falcon concentrator are returned to the final concentrate pump box to minimise any gold losses from the gravity cleaning circuit.

The dried gravity concentrates are mixed in batches with fluxes designed to allow the best separation of the gold and silver into doré. These batches are smelted and poured into moulds to produce

Water Supply

Summary:

Raw water is currently sourced from the underground mine dewatering discharge water that has undergone solids removal via coagulant and flocculant addition, followed by flow through four settling ponds. Part of this discharge is from a pair of production bores located outside the completed open pit. These bores pump water to the mine dewatering tank which transfers water to the plant raw water tank for use in gland water systems, gravity and gold room operation, reagent mixing and potable water treatment. Raw water requirement is approximately 80 m3 /h.

Process water is recovered from within the plant from the tailings and concentrate thickeners with makeup sourced from the TSF pond at 340m3 /h. Recycle rates of process water are high, exceeding 80% with the only raw water makeup into the system from services requiring higher quality water.

The Paste Plant requires approximately 140m3 /h clean water supply for its operation. To supply this requirement, underground dewatering water is used. This is pumped through several stages of ponds intended for turbidity treatment before most of it is released to environment and part of it is directed to mine dewatering tank that supplies the Paste Plant.

Since 2018, all water used in the processing plant is recycled, utilizing both the overflow water from thickeners and decantwater from the TSF tailings pond.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Consultant - Mining & Costs	Phil Jones		Dec 31, 2021
General Manager	David Bickerton		Aug 14, 2024
Sr. Project Manager	Glen Duncan		Aug 14, 2024
Study Manager	Glen Taylor		Aug 14, 2024
Technical Services Manager	Philip Jones		Aug 14, 2024
Underground Mine Manager	Daniel Calderwood		Aug 14, 2024