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OceanaGold Files Preliminary Prospectus for Didipio Initial Public Offering and Provides Underground Optimization Update, 2023 Reserves and Resources and Exploration Update at Didipio

Financings Resource Estimates Exploration Programs

www.oceanagold.com

February 2, 2024 News Release

OceanaGold Files Preliminary Prospectus for Didipio Initial Public Offering

and Provides Underground Optimization Update, 2023 Reserves and

Resources and Exploration Update at Didipio

(VANCOUVER) OceanaGold Corporation (TSX:OGC, OTCQX:OCANF) (“OceanaGold” or the “Company”)

is pleased to announce that i ts wholly owned subsidiary, OceanaGold Philippines, Inc. (“OGPI”), has filed a

registration statement and draft preliminary prospectus with the Philippine Securities and E xchange

Commission (“SEC”) and a listing application with The Philippine Stock Exchange, Inc. (“PSE”) in relation to the

proposed initial public offering (the “Offering”) of 20% of the outstanding common shares of OGPI. OGPI

holds the Company’s interest in the Didipio Mine and, pursuant to the terms of the renewed Financial or

Technical Assistance Agreement (“FTAA”), is required to list its common shares on the PSE. The Offering

is a secondary offering of common shares, with the proceeds to be received by a wholly owned subsidiary

of OceanaGold.

OceanaGold is also providing an update on the recently completed Didipio underground optimization work

(the “Underground Optimization”), the year -end 2023 Mineral Reserves and Mineral Resources estimate

for Didipio, and recent exploration and resource conversion results at Didipio.

Gerard Bond, President and CEO of OceanaGold, said, “We are proud of Didipio’s track record as a proven

high-quality, long -life, low -cost gold -copper mine and look forward to welcoming new Filipino and

international shareholders to participate in the expected robust free cash flow generation , consistent

dividend payments, and future potential at Didipio.

Today’s release highlights the upside potential we see at Didipio, including findings from the Underground

Optimization work and further exploration and resource conversion success as we look to replace and add

additional reserves and resources. We believe that the future at Didipio i s bright and look forward to it

continuing to create value for both OceanaGold and our new OGPI shareholders.”

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OGPI Initial Public Offering

OGPI has filed a registration statement and draft preliminary prospectus with the SEC for the Offering of 20%

of OGPI’s common shares, with the Offering expected to be completed prior to July 2024. OGPI holds the

Company’s interest in the Didipio Mine and, pursuant to the terms of the renewed FTAA, is required to list

at least 10% of its common shares on the PSE. Due to the PSE’s minimum public float requirement of 20%,

OGPI intends to list all of its issued and outstanding common shares and publicly float 20% thereof on the

main board of the PSE.

The Offering , which is subject to receipt of Philippine regulatory approvals , operating performance and

market conditions, will comprise a secondary offering of common shares of OGPI, with the proceeds to be

received by a wholly owned subsidiary of OceanaGold. The proposed Offering price will be determined in

the context of the market through a book building process with a maximum up-to price of ₱17.28 per share

(US$0.31 per share), and a maximum sale of 456,000,000 common shares. The Offering is being led by

BDO Capital & Investment Corporation as Global Coordinator and Domestic Underwriter and Bookrunner,

with CLSA Limited as International Underwriter.

To comply with Philippine regulatory requirements, the draft preliminary prospectus , which contains

important information in relation to the Offering, and accompanying Philippine Mineral Reporting Code

technical report with res pect to the Didipio Mine , have been made available to Philippine residents on

https://www.didipiomine.com.ph/. The Company notes that its technical report title d “NI 43-101 Technical

Report Didipio Gold/Copper Operations Luzon Island, Philippines” dated March 31, 2022 with an effective

date of December 31, 2021 (the “Didipio Technical Report”) , which is available on SEDAR+ at

www.sedarplus.com and the Company’s website , remains the Company’s current technical report for the

purposes of National Instrument 43-101 – Standards of Disclosure for Mineral Projects (“NI 43-101”).

Didipio Underground Optimization Update

The Underground Optimization work assessed the potential for increased underground mining rates, as

well as potential resource extensions below the current reserve limit of Panel 2 (2100 mRL). Preliminary

findings include:

• The potential to increase total underground material movement to approximately 2.5Mtpa (from the

current 1.75Mtpa), displacing lower grade stockpile ore and thereby increasing the overall feed

grade to the mill;

• The potential to increase mill throughput from the current 4.0Mtpa to the already permitted 4.3Mtpa

to maximize the benefit of processing the larger volume of higher-grade underground ore;

• The potential to extend mine life and increase gold and copper production through further resource

conversion drilling and extension drilling in Panels 3 and 4 and below;

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• Estimated additional life-of-mine growth capital of between US$100 million and US$130 million for

additional mine development, expansion of the mobile equipment fleet, paste fill plant upgrade,

dewatering and ventilation; and

• The potential to generate a strong return on this growth capital through increased gold and copper

production and extended mine life.

There is no certainty , nor can OceanaGold provide any assurance, that the results of the Underground

Optimization will be realized, in part or at all . The findings of the work will require further assessment and

analysis, including further resource extension and conversion drilling, and the Company intends to complete

this work with the target to publish a NI 43-101 technical report in the first half of 2025, which is expected

to include:

• Detailed mine planning and trade off analysis of higher underground production rates and optim al

cut-off grade to support the increased underground material movement target;

• Detailed design and cos t estimates for increased mobile equipment, paste plant, ventilation, and

dewatering infrastructure;

• A power demand study for additional underground infrastructure, and an analysis of potential

equipment electrification to meet carbon reduction commitments;

• Detailed definition of the implementation plan to deliver the projected operational availability and

utilization improvements underpinning the increased production; and

• An updated Mineral Resource estimate to include the results of new drilling intended to extend and

increase confidence in the Mineral Resources in Panel 3 and Panel 4 below the current reserves

level (~2100 mRL).

Didipio Year-End 2023 Mineral Reserves and Resources

The Proven and Probable Mineral Reserves estimates at December 31, 2023 at Didipio are presented in

Table 1 below . The year-over-year 0. 08 Moz decrease in Mineral Reserves was due to 2023 mining

depletion, partially offset by conversion of underground resources.

Total open pit stockpiles at Didipio are comprised of Proven Mineral Reserves of 12.7 Mt at 0.38 g/t Au and

0.35% Cu (mined to a 0.4 g/t AuEq cut-off) with an additional stockpile of 5.3Mt at 0.18 g/t Au and 0.15%

Cu (mined to an approximate 0.27g/t AuEq cut-off).

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Table 1: Didipio Mineral Reserves for Year-End 2023

RESERVES

PROVEN PROBABLE PROVEN & PROBABLE

Mt Au g/t Ag g/t Cu % Mt Au g/t Ag g/t Cu % Mt Au g/t Ag g/t Cu % Au Moz Ag Moz Cu Mt Cut-Off

Open Pit Stockpiles 18.0 0.32 2.0 0.29 . . . . 18.0 0.32 2.0 0.29 0.18 1.2 0.05 0.40 g/t AuEq

Underground 14.6 1.56 1.9 0.43 5.9 0.95 1.6 0.36 20.5 1.38 1.8 0.41 0.91 1.2 0.08 0.76 g/t & 1.16 g/t

AuEq

DIDIPIO TOTAL 32.6 0.87 1.9 0.35 5.9 0.95 1.6 0.36 38.6 0.88 1.9 0.35 1.10 2.3 0.14

• Mineral Reserves defined by mine designs based upon metal prices of US$1,500/oz gold, US$3.00/lb copper and US$17/oz silver.

• Reported estimates of contained metal are not depleted for processing losses. Cut -offs are applied to diluted grades.

• Incremental stopes proximal to development already plan ned to access main stoping areas are reported at a lower cut -off of 0.76g/t AuEq, where

AuEq = Au g/t + 1.38 x Cu%.

The Measured, Indicated and Inferred Mineral Resources (inclusive of Mineral Reserves) estimates at

December 31, 2023 at Didipio are presented in Table 2 below. The year-over-year 0.11 Moz increase in

Mineral Resources was due to 0.27 Moz of resource growth in the underground due to successful resource

conversion and extensional drilling, partially offset by 2023 mining depletion of 0.16 Moz.

Table 2: Didipio Mineral Resources for Year-End 2023

RESOURCES

MEASURED INDICATED MEASURED & INDICATED

Mt Au g/t Ag g/t Cu % Mt Au g/t Ag g/t Cu % Mt Au g/t Ag g/t Cu % Au Moz Ag Moz Cu Mt Cut-Off

Open Pit Stockpiles 18.0 0.32 2.0 0.29 . . . . 18.0 0.32 2.0 0.29 0.19 1.2 0.05 0.40 g/t AuEq

Underground 15.0 1.70 2.1 0.46 14.8 0.92 1.5 0.34 29.8 1.31 1.8 0.40 1.26 1.7 0.12 0.67 g/t AuEq

DIDIPIO TOTAL 33.0 0.95 2.0 0.37 14.8 0.92 1.5 0.34 47.8 0.94 1.9 0.36 1.44 2.9 0.17

INFERRED

Mt Au g/t Ag g/t Cu % Au Moz Ag Moz Cu Mt Cut-Off

Underground 12 0.8 1.3 0.3 0.30 0.5 0.03 0.67 g/t AuEq

DIDIPIO TOTAL 12 0.8 1.3 0.3 0.30 0.5 0.03

• Mineral Resources are reported inclusive of Mineral Reserves. Mineral Resources that are not Mineral Reserves do not have demonstrated

economic viability. Due to the uncertainty that may be attached to Inferred Mineral Resources, it cannot be assumed that all or any part of an Inferred

Mineral Resource will be upgraded to an Indicated or Measured Mineral Resource as a result of continued exploration.

• Underground Mineral Resources estimate is reported within optimised stope designs, above 1,800mRL, based upon metal prices of US$1,700/oz

gold, US$350/lb copper and US$20/oz silver.

• Underground Mineral Resources are estimated at 0.67 g/t AuEq cut off, where AuEq = Au g/t + 1.39 x Cu%.

• Open pit stockpiles include 5.3 Mt of low grade at 0.27 g/t AuEq cut -off.

Didipio Exploration Update

The Didipio alkalic Cu-Au porphyry deposit comprises a series of mineralised intrusions (monzonite,

monzonite porphyry, pegmatite (Balut) dyke, feldspar porphyry, syenite porphyry) and associated quartz

and monomictic breccias within a diorite stock (Figure 1).

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Figure 1: Didipio simplified geology 3D block cut.

Since the Company’s news release dated August 15, 2023, 5,343 meters (“m”) of resource conversion and

extensional drilling in twenty-two holes has been completed from underground (Figure 2).

Figure 2: Plan showing H2 2023 drilling with significant intercepts, simplified geology and mineralized zones >0.67g/t AuEq

at 2190mRL. Sections A-A’ through D-D’ also shown.

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Extension Drilling

Resource extensional drilling in H2 2023 focused on: testing for the Balut Dyke on the northern side of the

Syenite Porphyry (Figure 3) and following up on the success of the late-2022 drilling which discovered the

mineralized Eastern Breccia and Feldspar Porphyry in the east (Figure 4).

Testing of the Balut Dyke below 1980mRL and to the north of the Syenite Porphyry has returned a positive

result intersecting disseminated and clots of chalcopyrite and bornite in an actinolite pegmatite returning

45.4m @ 2.51g/t AuEq in RDUG500; a similar thickness and grade to previous intercepts of the Balut Dyke

south of the Syenite Porphyry and at higher elevations ( Figure 3). Mineralization of the newly discovered

pegmatite remains open along strike and at depth while its analogue on the sout h remains open at depth.

Two additional mineralized intrusives to the east were discovered in 2022 (Eastern Breccia and Feldspar

Porphyry) and were further tested during the H2 2023 drilling program (Figure 4). The Eastern Breccia, an

intrusive breccia with monzonite and diorite clasts, contains a significant amount of Cu -Au mineralization

which occurs as fine dissemination and su lphide veins within an intensely altered potassic zone. The

Eastern Breccia remains unexplored below 2000mRL. Mineralization in the other mineralized intrusive, the

Feldspar Porphyry Intrusion, has been extended a further 100m vertically.

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Figure 3: Section showing H2 2023 drilling with significant intercepts associated with the Monzonite, Balut Dyke, and

Syenite Porphyry.

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Figure 4: Section showing H2 2023 drilling with significant intercepts associated with the Eastern Breccia and Feldspar

Porphyry Intrusion.

Conversion Drilling

Resource conversion drilling in H2 2023 focused on conversion of the Inferred Mineral Resources within

the Monzonite Porphyry directly east of the Syenite Porphyry within Panel 2 (>2100mRL) and Panel 3 (<

2100mRL, Figure 5) and conversion of Inferred material within the Balut Dyke to the south of the Syenite

Porphyry (Figure 4 and Figure 6).

Drilling has converted 0.27 Moz of Inferred Mineral Resources to Indicated Mineral Resources within the

Monzonite Porphyry and Balut Dyke, providing improved confidence within Panel 3 between ~2100mRL

and 2000mRL, and demonstrating continuity of relatively high-grade porphyry Cu-Au mineralization within

the Monzonite Porphyry east of the Syenite Porphyry (Figure 5).