Oceanagold Reports Mineral Resources and Reserves FOR the Year Ended 2022

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31 March 2023 News Release

OCEANAGOLD REPORTS MINERAL RESOURCES AND RESERVES

FOR THE YEAR ENDED 2022

(VANCOUVER) OceanaGold Corporation (TSX:OGC) ( “OceanaGold” or the “Company”) is pleased to

provide its Resource and Reserve (“R&R”) statement for the year-ended 31 December 2022.

Gerard Bond, President and CEO of OceanaGold said, “Our Reserves and Resources continue to provide

a solid foundation for OceanaGold, underpinning our growth in gold production over the coming years. In

2022, w e continue d to have success delineating the underground potential at Haile , as evidenced by

resource additions at both Horseshoe and Palomino . We also successfully added resource ounces at

Didipio, with limited drilling, and Golden Point Underground at Macraes. While resource conversion drilling

at Wharekirauponga was impacted by restrictions associated with drought conditions in 2022, we expect to

continue delineating this deposit in 2023.

We are excited about our continued resource conversion and growth opportunities at Haile Underground,

Didipio, Martha Underground and Wharekirauponga, and have increased our near-mine exploration budgets

by over 35% for 2023.”

Highlights

• Increased Indicated Resources by 0.18 Moz at Palomino Underground, Haile, USA.

• Increased Inferred Resources by 0.16 Moz at Horseshoe Underground, Haile, USA.

• Increased Inferred Resources by 0.16 Moz at Golden Point Underground, Macraes, New Zealand.

• 0.05 Moz increase in Indicated Resources in Panel 2, Didipio, Philippines.

• Total Proven and Probable Reserves stood at 5.20 Moz gold (124 Mt at 1.30 g/t gold), including 7.4

Moz silver and 0.15 Mt copper.

• Total Measured and Indicated Resources, inclusive of Mineral Reserves , stood at 8.59 Moz gold

(186 Mt at 1.44 g/t gold), including 13 Moz silver and 0.17 Mt copper.

• Total Inferred Resources stood at 3.9 Moz of gold (59 Mt at 2.1 g/t gold) , largely un-changed year-

over-year as in creases at Golden Point Underground, Horseshoe Underground, and Martha

Underground offset conversion to Indicated Resources success at Palomino.

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Total Mineral Reserves

As at December 31, 2022, OceanaGold’s Proven and Probable ( “P&P”) Reserves stood at 1 24 Mt at 1.30

g/t gold for 5.20 Moz of gold, including 7.4 Moz of silver and 0.15 Mt of copper, representing a 0.43 Moz

decrease in gold Reserves year-over-year (see Table 1), largely due to mining depletion.

Table 1: Mineral Reserves (as at December 31, 2022)

Figure 1: Changes to Total Proven & Probable Mineral Reserves

PROJECT

AREA Cut-Off 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

HAILE Open Pit 0.50 g/t & 0.60 g/t Au 4.2 1.20 1.7 . 36.3 1.60 2.4 . 40.5 1.56 2.3 . 2.03 3.0 .

HAILE Underground 1.72 g/t Au . . . . 3.4 3.91 . . 3.4 3.91 . . 0.42 . .

USA 4.2 1.20 39.6 1.80 43.8 1.74 2.45 3.0 .

DIDIPIO Open Pit 0.40 g/t AuEq 20.8 0.33 2.0 0.31 . . . . 20.8 0.33 2.0 0.31 0.22 1.3 0.06

DIDIPIO Underground 0.76 g/t & 1.16 g/t AuEq 11.6 1.80 2.0 0.45 8.57 1.06 1.7 0.36 20.2 1.48 1.9 0.41 0.96 1.2 0.08

PHILIPPINES 32.4 0.85 8.6 1.06 41.0 0.90 1.18 2.5 0.15

MACRAES Open Pit 0.40 g/t Au 5.3 0.62 . . 27.4 0.88 . . 32.7 0.83 . . 0.88 . .

MACRAES Underground 1.31 g/t & 1.47 g/t Au 0.16 1.95 . . 2.85 1.93 . . 3.01 1.93 . . 0.19 . .

WAIHI Open Pit . . . . . . . . . . . . . . .

WAIHI Underground 2.60 g/t & 3.10 g/t Au 0.00 2.00 14.5 . 3.81 4.16 15 . 3.81 4.16 15 . 0.51 1.8 .

NEW ZEALAND 5.5 0.66 34.0 1.33 39.5 1.24 1.57 1.8 .

TOTAL 42.1 0.86 82.2 1.53 124 1.30 5.20 7.4 0.15

PROVEN PROBABLE PROVEN & PROBABLE

Mineral Reserves constrained to mine designs based upon US$1,500/oz gold, US$3.00/lb copper and US$17/oz silver. New Zealand reserves use 0.70 NZD/USD exchange rate.

Reported estimates of contained metal are not depleted for processing losses.

For underground reserves, cut-offs applied to diluted grades.

For Haile Open Pit, the primary cut-off grade is 0.5 g/t Au whilst oxide material is assigned a 0.6 g/t Au cut-off grade.

For Haile Underground, the cut-off is 1.72 g/t Au, with adjacent lower grade stopes included in the reserves based on an incremental stope cut-off grade of 1.56 g/t Au.

For Waihi Underground, the cut-off for previously unmined stoping areas is 2.6 g/t Au, increasing to 3.1 g/t Au for stoping areas in close proximity to remnant workings.

For Didipio the 20.8 Mt open pit stockpile inventory includes 5.3 Mt of low grade stocks mined at an approximate 0.27 g/t AuEq cut-off.

For Didipio, gold equivalence is based upon the presented gold and copper prices as well as processing recoveries. AuEq = Au g/t + 1.37 x Cu%.

For Didipio Underground, incremental stopes proximal to development already planned to access main stoping areas are reported to a lower cut-off of 0.76 g/t AuEq.

For Macraes Underground, Frasers Underground cut-off is 1.31 g/t Au whilst Golden Point Underground cut-off is 1.47 g/t Au.

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Total Mineral Resources

As at December 31, 2022, OceanaGold’s Measured and Indicated ( “M&I”) Resources stood at 1 86 Mt at

1.44 g/t gold for 8.59 Moz of gold, including 1 3 Moz of silver and 0.1 7 Mt of copper (Table 2 ). Mineral

Resources are reported inclusive of Mineral Reserves.

Table 2: Measured and Indicated Mineral Resources (as at December 31, 2022)

On a consolidated basis, M&I Resources decreased by 0.54 Moz relative to year -end 2021 (Figure 2 ).

Decreases were due to mining depletion across the Company’s operations , as well as revised resource

classification and mining assumptions at Martha Undergrou nd and slight reduction in the open pit resource

due to increase d cost inputs at Haile . The decreases were partially offset by gains due to resource

conversion drilling at Palomino, Golden Point Underground, and Didipio.

PROJECT

AREA Cut-Off 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

HAILE Open Pit 0.45 g/t / 0.55 g/t Au 4.5 1.17 1.2 . 38.4 1.55 2.5 . 42.9 1.51 2.4 . 2.09 3.3 .

HAILE Underground 1.37 g/t & 1.49 g/t Au . . . . 7.0 3.97 . . 7.0 3.97 . . 0.90 . .

USA 4.5 1.17 45.4 1.93 49.9 1.86 2.98 3.3 .

DIDIPIO Open Pit 0.40 g/t AuEq 20.8 0.33 2.0 0.31 . . . . 20.8 0.33 2.0 0.31 0.22 1.3 0.06

DIDIPIO Underground 0.67 g/t AuEq 11.6 1.86 2.1 0.48 12.6 1.03 1.7 0.37 24.2 1.43 1.9 0.42 1.11 1.5 0.10

PHILIPPINES 32.4 0.88 12.6 1.03 45.0 0.92 1.33 2.8 0.17

MACRAES Open Pit 0.30 g/t Au 16.5 0.92 . . 52.6 0.72 . . 69.2 0.77 . . 1.71 . .

MACRAES Underground 1.28 g/t / 1.15 g/t Au 0.3 2.56 . . 6.7 2.33 . . 7.0 2.35 . . 0.53 . .

BLACKWATER

WAIHI Open Pit 0.5 g/t / 0.56 g/t Au . . . . 7.2 1.73 13 . 7.2 1.73 13 . 0.40 2.9 .

WAIHI Underground 2.15 g/t / 2.50 g/t Au . . . . 7.3 6.94 19 . 7.3 6.94 19 . 1.64 4.5 .

NEW ZEALAND 16.9 0.95 73.9 1.58 90.7 1.46 4.27 7.4 .

TOTAL 53.8 0.93 132 1.65 186 1.44 8.59 13 0.17

For Didipio Open Pit, only stockpiles remain. These include 5.3 Mt of low grade at at 0.27 g/t AuEq. Underground resources reported at a 0.67 g/t AuEq cut-off between the 2,460mRL and

1,980mRL with gold equivalence (AuEq) cut-off based on presented gold and copper prices. AuEq = Au g/t + 1.39 x Cu %.

Macraes: Frasers Underground at a 1.28 g/t Au cut-off and Golden Point Underground at a 1.15 g/t Au cut-off.

Waihi: Martha Underground M&I Resources 5.7 Mt @ 5.35 g/t Au for 0.97 Moz. WKP M&I resources 1.7 Mt @ 12.3 g/t Au for 0.66 Moz

Waihi: Martha Underground at a 2.15 g/t Au cut-off, WKP at a 2.5 g/t Au cut-off, Martha Open Pit at a 0.5 g/t Au cut-off and Gladstone Open Pit at a 0.56 g/t Au cut-off.

Haile Open Pit primary cut-off 0.45 g/t Au, oxide cut-off 0.55 g/t Au. Palomino Resources at a 1.49 g/t Au cut-off and Horseshoe Resources at a 1.37 g/t Au cut-off, the difference due to

slightly lower metallurgical recovery at Palomino

Open Pit resources constrained to shells based upon economic assumptions above. Waihi Open Pit resources reported within a pit design limited by infrastructural considerations.

Underground resources for Didipio, Horseshoe at Haile, and Frasers and Golden Point at Macraes, are reported within volumes guided by optimised stope designs. Underground

resources for Palomino at Haile and Martha and WKP at Waihi are reported within optimised stope designs based upon economic assumptions above

All resources based upon US$1,700/oz gold, US$3.50/lb copper and US$20/oz silver and a 0.70 NZD/USD exchange rate for New Zealand resources.

Mineral Resources include Mineral Reserves. There is no certainty that Mineral Resources, not included as Mineral Reserves, will convert to Mineral Reserves

MEASURED INDICATED MEASURED & INDICATED

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Figure 2: Changes to Total Measured & Indicated Mineral Resources

As at December 31, 2022, Inferred Resources stood at 59 Mt at 2.1 g/t gold for 3.9 Moz of gold, including

7.3 Moz of silver and 0.04 Mt of copper ( Table 3). No net change year -over-year. Increases in Inferred

Resources for Golden Point Underground, Horseshoe Underground, and Martha Underground were offset

by decreases for Palomino . The Palomino decreases in Inferred Resources resulted from conversion to

Indicated Resources.

Table 3: Total Inferred Mineral Resources (as at December 31, 2022)

PROJECT

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

HAILE Open Pit 0.45 g/t / 0.55 g/t Au 4.0 0.9 2.3 . 0.1 0.3 .

Haile Underground 1.37 g/t & 1.49 g/t Au 4.8 3.9 . . 0.6 . .

USA 9 2.6 0.7 0.3 .

DIDIPIO Open Pit 0.40 g/t AuEq . . . . . . .

DIDIPIO Underground 0.67 g/t AuEq 15 0.9 1.4 0.3 0.4 0.6 0.04

PHILIPPINES 15 0.9 0.4 0.6 0.04

MACRAES Open Pit 0.30 g/t Au 20 0.7 . . 0.5 . .

MACRAES Underground 1.28 g/t / 1.15 g/t Au 2.9 2.0 . . 0.2 . .

BLACKWATER Geological 0.9 23 . . 0.7 . .

WAIHI Open Pit 0.5 g/t / 0.56 g/t Au 5.7 1.7 16 . 0.3 3.0 .

WAIHI Underground 2.15 g/t / 2.50 g/t Au 5.9 6.1 18 . 1.2 3.4 .

NEW ZEALAND 36 2.4 2.8 6.4 .

TOTAL 59 2.1 3.9 7.3 0.04

See footnotes for Table 2.

INFERRED

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Figure 3: Changes to Total Inferred Resources

Haile, USA

P&P Reserves at Haile totalled 43.8 Mt at 1.74 g/t gold for 2.45 Moz of gold , including 3.0 Moz of silver.

Year-over-year, P&P Reserves have decreased 0. 11 Moz due to mining depletion (Figure 4). Of the 2.45

Moz of gold, the Horseshoe Underground contributes 0.42 Moz (3.4 Mt at 3.9 g/t gold).

Figure 4: Changes to Haile Proven & Probable Mineral Reserves

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Total Haile M&I Resources stood at 49.9 Mt at 1.86 g/t gold for 2.98 Moz of gold, including 3.3 Moz of silver.

A slight 0.06 Moz decrease relative to 2021 year-end, which is largely due to open pit depletion and increased

operating costs (Figure 5), offset by resource growth at Palomino and Mill Zone Stage 2 open pit.

Of the 2.98 Moz of gold, underground contributes 0.90 Moz which includes both Horseshoe and Palomino

deposits. Resource conversion drilling during 2022 at Palomino increased Indicated Resources by 0.18 Moz,

delivering an updated Indicated Resource of 3.7 Mt at 3.15 g/t for 0.38 Moz. Resource conversion drilling at

Palomino planned for 2023 continues to target the remaining 0.15 Moz of Inferred Resource. An economic

study for Palomino is planned for 2023 with the objective being to convert this material to reserves around

year-end.

Figure 5: Changes to Haile Measured & Indicated Mineral Resources

Haile Inferred Resources remained at 9 Mt at 2.6 g/t gold for 0.7 Moz gold. Decreases due to conversion of

Inferred Resources at Palomino and Mill Zone were offset by resource growth at Horseshoe (Figure 6).

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Figure 6: Changes to Haile Inferred Resources

Haile Resource Model Performance

Table 4 summarizes the Haile open pit resource model reconciliations from 2018 to 202 2. The resource

model to mill-adjusted mine reconciliation data shows variable performance from year to year, albeit the long

term five-year average performance is reasonable; +11% for tonnes, 0% for grade and +11% for contained

gold. The positive reconciliation for 2022 was largely due to realizing more gold within, and adjacent to,

historically mined areas within the Haile Stage 1 open pit cut-back. Mining of this pit stage was completed in

September 2022. Open pit mining continues in the Mill Zone and Ledbetter areas.

While annual reconciliation fluctuations are expected to continue, the Haile open pit resource estimates are

believed to provide an acceptable basis for medium to long term mine planning purposes.

Table 4: Haile Open Pit Resource Model Performance, 2018 to 2022

Mt Au g/t Moz Mt Au g/t Moz Mt Au g/t Moz

2022 3.39 1.59 0.17 4.13 1.76 0.23 122% 110% 134%

2021 3.16 1.98 0.20 3.27 2.17 0.23 103% 110% 115%

2020 2.57 2.08 0.17 3.33 1.59 0.17 130% 76% 100%

2019 2.87 1.96 0.18 3.18 1.78 0.18 111% 91% 100%

2018 2.85 1.67 0.15 2.57 1.93 0.16 90% 116% 107%

TOTAL 14.8 1.83 0.87 16.5 1.84 0.97 111% 100% 111%

Resource Model Mine (Mill-Reconciled) Mine / Model Factor (%)

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Didipio, Philippines

Didipio P&P Reserves stood at 41.0 Mt at 0.90 g/t gold for 1.18 Moz of gold, including 2.5 Moz of silver and

0.15 Mt of copper, a slight year-over-year 0.05 Moz decrease due to 2022 mining depletion ( Figure 7),

partially offset by resource growth in the underground.

Figure 7: Changes to Didipio Proven & Probable Mineral Reserves

Didipio M&I Resources stood at 45.0 Mt at 0.92 g/t gold for 1.33 Moz of gold, including 2.8 Moz of silver and

0.17 Mt of copper, a 0.08 Moz year-over-year decrease due to 2022 mining depletion partially offset by

resource growth (Figure 8).

At Didipio a total of 15.5 Mt at 0.38 g/t gold and 0.36% copper remains in stockpiles (mined to a 0.4 g/t AuEq

cut-off) with an additional stockpile of 5.3 Mt at 0.18 g/t gold and 0.15% copper (mined to an approximate

0.27 g/t AuEq cut-off).