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OceanaGold Mines First Ore from Horseshoe Underground and Provides Haile Operations and Exploration Update

Mine Development & Operations Exploration Programs

September 14, 2023

News Release

OceanaGold Mines First Ore from Horseshoe Underground and Provides

Haile Operations and Exploration Update

(VANCOUVER) OceanaGold Corporation (TSX: OGC) (“OceanaGold” or the “Company”) announces that

it has mined first development ore from the Horseshoe Underground and is on track to deliver first stope

ore in October 2023 at its Haile Gold Mine (“Haile”) in the United States . The Company also provides an

update in respect to open pit operations and exploration activities at Haile.

Highlights:

• First development ore has been mined from the Horseshoe Underground mine and first stope

production is expected in October with ramp-up to occur through the fourth quarter and first half of

2024. Grade control drilling at Horseshoe Underground has delivered results in- line with or above

model expectation to date.

• Haile’s third quarter 2023 gold production has been adversely impacted by lower than estimated

ore grades encountered in the now-completed Mill Zone pit . We now expect Haile’s third quarter

gold production to be around 23,000 ounces, and Haile’s full-year production to be around 25,000

ounces below 2023 guidance ranges. With strong operating performance expected at Didipio and

Macraes, expected full-year consolidated gold production for the Company remains within the lower

end of the original guidance range.

• Haile 2023 resource definition and exploration campaign highlights include (core length):

o 73.9m @ 13.03 g/t Au (UGD0002) – Horseshoe Underground (resource conversion)

o 7.5m @ 3.65 g/t Au (DDH1177) – Palomino (extension)

o 6.3m @ 2.89 g/t Au (DDH1173) – Palomino (extension)

Gerard Bond, President & CEO of OceanaGold, said “We are pleased to have mined first development ore

from the Horseshoe Underground. The team has done a tremendous job in planning and safely executing

the work to deliver this important growth project. We remain on track to have first stoping ore in October

and will then ramp up to full target mining rates through the first half of 2024. The future of Haile continues

to be exciting and with the release of today’s drilling results, including a high grade resource conversion

result in the Horseshoe inferred resource, it is clear that there continues to be considerable upside to our

current plan.”

David Londono, Chief Operating Officer Americas, said “Although mining from Mill Zone in 2023 has been

disappointing through the second and third quarter, the reconciliation challenges encountered are in a

localized area within Mill Zone pit where mining is now complete, and mining has now shifted to Ledbetter

Phase II. Previous phases of the Ledbetter pit have reconciled well versus our resource model, and we

remain confident in our long-term production profile for the mine, particularly with Horseshoe Underground

becoming a meaningful contributor in 2024 and beyond.”

Horseshoe Underground Achieves First Ore

Development of the Horseshoe Underground has progressed with approximately 2,230 metres (“m”) of total

development to date. Lateral development is well advanced on the 1025 and 1000 levels, and the decline

has progressed down to the 975 level. Development ore equating to ~3,800 tonnes from the 1025 level

(figure 1) has been mined and currently stockpiled on surface for processing.

Figure 1: Plan view of 1025 level (A) and 1000 level (B) showing actual development (light blue) and

planned development (dark blue) as at September 11, 2023.

Three stopes are planned to be mined in 2023 , commencing in October. Stopes sizes range from 25,000

to 35,000 tonnes and will be initially mined on the 1000 and 975 levels, with total stope ore production

expected to contribute approximately 90,000 tonnes to the mine plan in 2023 (figure 2). Underground

stoping is expected to ramp-up in the fourth quarter and reach the full target mining rate by mid-2024.

Figure 2: Long section looking south-west of Horseshoe Underground with 2023 stopes highlighted in

dark blue

Grade control drilling on a 15m by 20m spacing is progressing from underground in advance of

development, with nine holes drilled to date. The holes are reconciling consistently well to the block model

and provide confidence in the resource as we approach our first stopes.

Haile Operations Update

As disclosed with our second quarter results, the short term mine plan at Haile was adversely impacted by

negative grade reconciliation in the lower levels of the Mill Zone pit . We now expect Haile’s third quarter

gold production to be approximately 23,000 ounces, and full-year production to be around 25,000 ounces

lower than 2023 guidance. We also expect Haile’s third quarter cash costs and AISC to be materially higher

due to the lower gold production.

Full-year 2023 guidance for Haile will be updated with the release of third quarter results . OceanaGold

continues to expect to be within full -year consolidated gold production guidance r ange for the Company

given the strong operating performance expected at Didipio and Macraes, albeit toward the lower end of

the range.

As per the 2023 mining schedule, mining at Mill Zone pit was completed in August 2023 and has shifted to

stripping Ledbetter Phase II. During the transition between pits, material to the mill is being fed from surface

stockpiles, with Horseshoe Underground and Ledbetter open pit progressively providing ore for processing

in the fourth quarter.

Despite poor grade reconciliation in the lower benches of Mill Zone pit in the second and third quarter of

2023, Mill Zone has reconciled in-line with resource model expectations (+1% ounces) since mining began

in 2018. Short-term negative reconciliation seen in the last two quarters is a combination of local variation

in grade and wider drill spacing at bottom benches of the pit. For more detail on Haile long term

reconciliation, please see 2022 Reserve and Resource news release dated March 31, 2023.

Haile Exploration Update

A program of resource definition and conversion drilling at Horseshoe Underground totalling ~18,400m is

in progress and is scheduled to be completed by the end of 2024. To date, conversion drilling totalling

2,617m in six holes has been completed, with an additional 2,600m planned by 2023 year end. Drilling has

targeted the conversion of the lower Horseshoe inferred resource with two holes to date, UGD0001 and

UGD0002. UGD0001 ha d substantial deviation and did not return a significant result , while UGD0002

returned 73.9 m @ 13.03 g/t Au, showing better than expected grade (table 1). The lower extension of the

Horseshoe resource remains open.

Resource conversion drilling continued at Palomino, located approximately 800 metres southwest of the

Horseshoe Underground mine, and where future access may be gained from underground infrastructure

(figure 3). Following data cut-off for the end of year 2022 Annual Resource and Reserve statement, 9,818m

and 19 holes of resource conversion drilling have been completed with all but two holes intersecting

mineralisation and returning results in lin e with expectations , including 60.4m @ 7. 95g/t Au in hole

DDH1164 and 40.0m @ 3.5 0g/t Au in hole DDH1189 (figure 3 and table 1). The Palomino resource

conversion program has now been completed with a resource model update scheduled in Q1 2024 following

receipt of all outstanding assays from the lab.

Twenty regional exploration holes within the mining lease have been drilled from surface in 2023 across

early-stage (Horsetail, Aquarius, Ramona, Capricorn) and extensional (Palomino) targets , testing the

prospective metasediment –metavolcanic contact where the contact is poorly defined or sparsely drilled

(figure 4). Two significant intercepts have been returned testing the northeast extension of the Palomino

deposit with hole DDH1177 intersecting 7.5m @ 3.65g/t Au from 527.7m and hole DDH1173 intersecting

6.3m @ 2.89 g/t Au from 483.5m (figure 3 and table 1) . Drilling at the Ledbetter extensional target has

commenced and remains in progress.

Figure 3: Long section (looking north-west) showing Palomino and Horseshoe with 2023 year-to-date

drilling with assays received

Figure 4: Completed 2023 YTD surface drill hole locations and targets

Table 1: Haile Drill Intersections. NSR = No Significant Result.

Hole ID From (m) To (m) Core Length

(m) Au g/t Target Drill Category

UGD0001 - - - NSR Horseshoe Resource Conversion

UGD0002 306.8 380.7 73.9 13.03 Horseshoe Resource Conversion

incl. 311.7 348.3 36.5 20.93 Horseshoe Resource Conversion

DDH1144 401.6 464.2 62.6 2.44 Palomino Resource Conversion

and 483.9 488.8 4.9 7.14 Palomino Resource Conversion

DDH1145 435.5 454.4 18.9 5.40 Palomino Resource Conversion

and 468.4 482.0 13.6 3.53 Palomino Resource Conversion

and 492.8 515.2 22.5 4.73 Palomino Resource Conversion

DDH1152 331.4 360.2 28.8 4.15 Palomino Resource Conversion

and 369.1 392.0 22.9 2.50 Palomino Resource Conversion

DDH1153 - - - NSR Palomino Resource Conversion

DDH1156 416.6 423.9 7.3 4.44 Palomino Resource Conversion

DDH1159 311.1 315.4 4.3 7.78 Palomino Resource Conversion

and 440.5 445.7 5.2 2.79 Palomino Resource Conversion

and 454.9 473.2 18.3 3.54 Palomino Resource Conversion

and 488.4 508.2 19.8 3.80 Palomino Resource Conversion

DDH1161 366.5 373.8 7.3 1.72 Palomino Resource Conversion

and 384.5 407.3 22.9 3.58 Palomino Resource Conversion

and 425.7 451.5 25.8 1.70 Palomino Resource Conversion

and 459.1 474.4 15.3 5.53 Palomino Resource Conversion

DDH1164 351.3 354.4 3.1 14.87 Palomino Resource Conversion

and 415.9 476.3 60.4 7.95 Palomino Resource Conversion

and 487.0 497.6 10.7 2.14 Palomino Resource Conversion

DDH1165 384.9 395.1 10.2 3.55 Palomino Resource Conversion

and 407.3 421.1 13.7 2.88 Palomino Resource Conversion

DDH1167 313.2 349.8 36.6 1.64 Palomino Resource Conversion

and 396.8 399.7 2.9 6.26 Palomino Resource Conversion

and 421.4 441.2 19.8 2.19 Palomino Resource Conversion

DDH1168 469.7 475.8 6.1 4.04 Palomino Resource Conversion

DDH1169 - - - NSR Palomino Resource Conversion

DDH1170 426.2 442.1 15.9 1.76 Palomino Resource Conversion

and 480.8 500.4 19.6 3.28 Palomino Resource Conversion

and 508.0 517.1 9.1 2.41 Palomino Resource Conversion

DDH1189 550.3 590.3 40.0 3.50 Palomino Resource Conversion

DDW1192 542.2 557.4 15.3 4.93 Palomino Resource Conversion

DDH1173 483.5 489.7 6.3 2.89 Palomino Extension

DDH1177 527.7 535.2 7.5 3.65 Palomino Extension

For further information relating to drill hole data for Haile please refer to the Company's website

at https://oceanagold.com/investor-centre/tsx-asx-filings.

For further information please contact:

Investor Relations:

Rebecca Harris, Director, Investor Relations

Tel: +1 604 678 4095

[email protected]

Media Relations:

Melissa Bowerman, Group Manager, Communications

Tel: +61 407 783 270

[email protected]

www.oceanagold.com | Twitter: @OceanaGold

About OceanaGold

OceanaGold is a growing intermediate gold and copper producer committed to safely and responsibly

maximizing the generation of Free Cash Flow from our operations and delivering strong returns for our

shareholders. We have a portfolio of four operating mines: the Haile Gold Mine in the United States of

America; Didipio Mine in the Philippines; and the Macraes and Waihi operations in New Zealand.

Qualified Person Statement

The exploration results in this press release were prepared in accordance with National Instrument 43-101

– Standards of Disclosure for Mineral Projects of the Canadian Securities Administrators ("NI 43- 101").

Information relating to the Haile exploration results in this document has been verified and is based on and

fairly represents information compiled by or prepared under the supervision of Craig Feebrey, a Member of

the Australasian Institute of Mining and Metallurgy and an employee of Oce anaGold. Mr Feebrey has

sufficient experience that is relevant to the style of mineralisation and type of deposit under consideration

and to the activity being undertaken to qualify as Qualified Persons for the purposes of the NI 43- 101. Mr

Feebrey consents to the inclusion in this public report of the matters based on their information in the form

and context in which it appears.

QA/QC at Haile Gold Mine

Since July 2017 all Haile exploration core samples have been prepared at the ALS lab in Tucson, Arizona,

and analysed at the ALS lab in Reno, NV. Samples are pulverized from a 450g sample to 85% passing 75

mesh. Approximately 225g of pulp sample is used for fire assay. Assays are based on a 30g fire assay

aliquot for gold with Atomic Absorption finish 3g/t Au. Some holes are composited and analysed for carbon,

sulphur and multi -elements using LECO and ICP -OES methods. ALS labs used for Haile OceanaGold

samples are ISO 17025 certified.

Blanks and standards are inserted every 20th sample. Check assays are s ubmitted to the SGS lab in

Kershaw, SC for 5% of the intervals each quarter. Assays are duplicated for >95% of the samples within

5% of their original assay. ALS samples show no evidence of contamination or instrument drift. Precision

and accuracy of CRMs compared to expected values have been consistently with 5% RSD and often within

3%. Graphs showing expected values and two standards of deviation have been produced and evaluated.

Barren marble and sand are inserted as blanks every 20th sample. Certified r eference materials from

RockLabs are inserted every 20th sample. All blanks and CRMs are handled by the Geotech Supervisor

and are stored in the locked OceanaGold office.

All drill hole samples are handled and transported from the drill rigs to the secur ed Haile Exploration

warehouse by OceanaGold personnel. Access to the property is controlled by locked doors and cameras

monitored by OceanaGold security. The main gate requires an electronic employee badge to enter.

Samples are packaged at the Haile Exploration warehouse by the Geotech Supervisor and geotechnicians.

Samples are trucked in sealed plastic barrels by certified couriers with submittal forms that are verified

during sample pick -up and delivery to ALS. No sample shipments have been recorded as m issing or

tampered with.

Technical Reports

For further information, please refer to the following NI 43-101 technical report:

a) “NI 43-101 Technical Report Haile Gold Mine Lancaster County, South Carolina” dated March 31,

2022, prepared by D. Carr, Chief Metallurgist, G. Hollett, Group Mining Engineer, and J. Moore,

Chief Geologist, each of OceanaGold Management Pty Limited, Michael Kirby of Haile Gold Mine,

Inc., J. Poeck, M. Sullivan, D. Bird, B. S. Prosser and J. Tinucci of SRK Consulting, J. Newton

Janney-Moore and W. Kingston of Newfields and L. Standridge of Call and Nicholas.

The above document has been filed with the Canadian securities regulatory authorities and is available for

review electronically from the Canadian System for Electronic Document Analysis and Retrieval (SEDAR)

at www.sedar.com under the Company’s profile.

Cautionary Statement for Public Release

Certain information contained in this public release may be deemed “forward- looking” within the meaning

of applicable securities laws. Forward-looking statements and information relate to future performance and