Results of Scout Drilling at Viuda Negra

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01 September 2025

Great Southern Copper plc

("GSC" or the "Company")

Scout Drill Results Confirm Discovery of Porphyry Gold System at Viuda Negra

First known occurrence of porphyry gold style mineralisation in Chile's coastal belt

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce results of its scout diamond drilling programme at Viuda Negra which confirms the discovery by GSC of a potentially large porphyry gold mineralised system.

Highlights:

· Scout diamond drilling at Viuda Negra targeted anomalous gold-silver results in outcrop1

· All drillholes intersected porphyry-style gold mineralisation with best intervals including;

o  DD004: 6.7m @ 0.39 g/t Au & 0.12% Cu from 43.1m, within broader interval of:

· 121.5m @ 0.11 g/t Au & 0.05% Cu from 6.5m, and

o  DD002: 14.2m @ 0.21 g/t Au & 0.11% Cu from 11m, within broader interval of:

· 73m @ 0.14 g/t Au & 0.1% Cu from 11m

· Results confirm discovery of a potentially large, near-surface porphyry gold system at Viuda

· Gold mineralisation occurs in stockworks of quartz veinlets characteristic of porphyry gold deposits in Chile's Maricunga Belt

· Maricunga type porphyry gold deposits not previously recognised in the coastal belt of Chile

· Gold grades closely related to fracture-vein density

· Highest fracture-vein densities and gold-copper grades consistent with observed mineralising porphyry intrusive and overprinting potassic quartz-magnetite alteration

· Mineralised system confirmed by drilling, mapping and rock chip sampling now measures 1.2 x 0.8 km in area and is open

· Results confirm exploration vectors to the southeast consistent with earlier scout RC drilling1

· Planning in progress for follow-up surface mapping, sampling and RC drilling

· Company holds options to own 100% of Viuda and Viuda Negra

· Viuda and Viuda Negra are part of the Especularita Project located in Chile's coastal metallogenic belt with excellent access and infrastructure

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "Porphyry gold deposits are large low-grade disseminated gold systems with project economics typically determined by size, depth, location and grade. These scout drilling results, at shallow depths and close to infrastructure, are therefore very significant, clearly demonstrating that the Viuda prospect hosts the potential for a large porphyry gold system and confirming the importance of Especularita within an emerging copper-gold district.

"Importantly, the drilling has provided strong exploration vectors toward a potentially higher grade centre of the system which will guide our follow-up work, and we are excited to advance to the next stage of exploration.

"With gold prices at historic highs we are looking forward to advance this exciting asset along-side our high-grade copper-silver project at Cerro Negro."

Viuda - Viuda Negra prospects:

The Viuda Negra and Viuda prospects, located approximately 15km to the southwest of the Company's Cerro Negro, comprises 18km2 of concessions centred upon a prominent hill of resistive silicified rock (Chingay Hill) and surrounded by a large (2km diameter) bowl-shaped depression ("bajo") of dominantly albite-pyrite-clay altered volcanics and intrusive rocks - a geological setting typical of many porphyry deposits, formed by supergene weathering and oxidation. The zoned, clay-rich alteration also produces a distinctive colour anomaly in spectral imagery (Figure 1).

Viuda Negra is located approximately 1km to the east of Chingay Hill, where recent scout reverse circulation ("RC") drilling intercepted zones of quartz-sulphide veinlets with pyrite-albite-clay and magnetite-albite -clay alteration grading up to 12m @ 1.5 g/t Au and 0.47% Cu1.

Figure 1: Viuda-Viuda Negra Prospects. Satellite image showing drill collars in relation to the large alteration-related colour anomaly

Results of Scout Diamond Drilling:

A total of four diamond drillholes for 553.05m were completed at Viuda Negra as part of a scout programme designed to test for mineralisation below outcropping ridges with anomalous gold and silver mineralisation defined by surface mapping and sampling1.

Drillhole VNE25-DD001 targeted outcropping sheeted Maricunga-style banded-quartz veinlets where previous channel sampling returned grades up to 4.2 g/t Au and 0.12% Cu1. The hole intercepted magnetite-albite-chlorite altered microdiorite intruded by intermediate-argillic altered diorite porphyry dykes and over-printed by stockworks of quartz fracture-vein alteration (5-10 banded veinlets per metre). Assays returned highly anomalous gold values associated with the stockwork alteration including 6.25m @ 0.17 g/t Au and 0.05% Cu from 36m.

Drillholes VNE25-DD002 and DD004 were collared 250m southeast of DD001 to test a prominent swarm of quartz veinlets within intensely silicified rocks, where surface sampling identified highly anomalous silver values up to 29.9 g/t Ag1. Both holes intercepted similar microdiorites cut by diorite porphyry dykes as in hole 001, but with significantly higher veinlet densities of up to 50 per metre.

Both holes returned broad intercepts of gold mineralisation with anomalous copper and silver, including;

o  DD004: 6.7m @ 0.39 g/t Au & 0.12% Cu from 43.1m, within broader interval of:

§ 121.5m @ 0.11 g/t Au & 0.05% Cu from 6.5m

§ Maximum assay of 0.55 g/t Au

o  DD002: 14.2m @ 0.21 g/t Au & 0.11% Cu from 11m, within broader interval of:

§ 73m @ 0.14 g/t Au & 0.1% Cu from 11m

The discrete higher-grade interval in DD004 is associated with a porphyritic microdiorite intrusive phase which is over-printed by abundant banded and A-type quartz veinlets and intense, magnetite-rich potassic alteration. This is interpreted as an early-mineral porphyry phase and suggests that higher-grade centres may be present elsewhere within the system.

Drillhole VNE25-DD003, drilled 100m northwest of DD002/DD004, intersected a shallow zone of veinlets and silica ledges within oxidised, leached rocks before passing into diorite porphyry and microdiorite with relatively low vein frequencies, thought to represent the edge of the main veinlet zone. The hole returned shorter intervals of gold mineralisation, including 3m @ 0.12 g/t Au from 1m and 15m @ 0.10 g/t Au from 8m.

The scout drilling confirms that gold and copper mineralisation is associated with stockwork and sheeted dark-banded and A-type quartz veinlets within widespread intermediate-argillic and magnetite-albite-chlorite altered diorite porphyry intrusives. The mineralisation and alteration are typical of Maricunga-style gold porphyry systems, such as Kinross Gold's Lobo-Marte deposit (6.7Moz Au at 1.3 g/t2), Maricunga (4.3 Moz at 0.7 g/t3) and Rio2's Fenix deposit (1.77 Moz Au at 0.48 g/t Au4).

Figure 2: Viuda Negra Prospect. Drillhole VNE25-DD004 - 57-60m. Stockwork and sheeted dark banded quartz veinlets. Assay 0.17 g/t Au.

Figure 3: Viuda Negra Prospect. Plan map showing drillhole locations, results and previously reported surface assays1

Figure 4: Viuda Negra Prospect. Section along drillholes showing stockwork zones, >0.1 g/t and >0.2 g/t Au intervals. System is open to the SE and with depth.

Next steps:

The gold-enriched stockwork alteration associated with a mineralising porphyry intrusive phase provides a strong exploration vector toward a potentially larger and high-grade core of the system located to the southeast of Viuda Negra. This result is consistent with the results of the earlier RC scout programme which suggested mineralisation was increasing toward the southeast.

Follow-up ground exploration including detailed mapping and sampling will be prioritised to target the next phase of RC exploration drilling to commence in the new year.

References:

1. RNS 2553F (16 April 2025): Scout RC Drilling at Viuda Confirms Potential for Mineralised Porphyry Style Au-Ag-Cu System

2. Kinross Gold 2024 Annual Mineral Resource and Resource Statement

3. Kinross Gold 2015 Annual Mineral Resource and Resource Statement

4. NI 43-101 Technical Report on the Feasibility Study for the Fenix Gold Project

Enquiries:

Notes for Editors:

About Great Southern Copper

Great Southern Copper PLC is a UK-listed mineral exploration company focused on the discovery of copper-gold-silver deposits in Chile. The Company has the option to acquire mining rights to 100% of Especularita project in the under-explored coastal belt of Chile that is prospective for large scale copper-gold-silver deposits. Chile is a globally significant mining jurisdiction being the world's largest producer and exporter of copper.

The Especularita Project is located in the coastal metallogenic belt of Chile which hosts significant copper mines and deposits, including Teck's Carmen de Andacollo copper mine, and boasts excellent access to infrastructure such as roads, power and ports. Significant historical small-scale and artisanal workings for both copper and gold are readily evident in the exploration project area. The coastal belt offers deposit type optionality for copper including porphyry and IOCG style deposits as well as newly recognised intrusive-related copper and gold deposits.

Great Southern Copper is strategically positioned to support the global market for copper - a critical battery metal in the clean energy transition around the world. The Company is actively engaged in exploration and evaluation work programmes targeting both large tonnage, low to medium grade Cu-Au as well as high-grade Cu-Ag-Au deposits.

Further information on the Company is available on the Company's website: https://gscplc.com

Competent Person Statement

The information in this announcement that relates to exploration results is based on and fairly represents information reviewed or compiled by Mr Sam Garrett, a Competent Person who is a Member of the Australian Institute of Geoscientists and a Fellow of the Society of Economic Geologists. Mr Garrett is the CEO and a shareholder of Great Southern Copper PLC. Mr Garrett has sufficient experience that is relevant to the styles of mineralisation and types of deposit under consideration and to the activity being undertaken to qualify as a Competent Person as defined in the 2012 Edition of the "Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves". Mr Garrett has provided his prior written consent to the inclusion in this announcement of the matters based on information in the form and context in which it appears.

This announcement includes information that relates to Exploration Results prepared and first disclosed under the JORC Code (2012) and extracted from the Company's previous LSE announcements as noted, and the Company's Prospectus dated 20 December 2021. Copies of these announcements are available from the LSE Announcements page of the Company's website: www.gscplc.com.

The Company confirms that it is not aware of any new information or data that materially affects the information included within the Prospectus dated 20 December 2021.

Forward Looking and Cautionary Statements

Some statements in this announcement regarding estimates or future events are forward-looking statements. They include indications of, and guidance on, future earnings, cash flow, costs and financial performance. Forward-looking statements include, but are not limited to, statements preceded by words such as "planned", "expected", "projected", "estimated", "may", "scheduled", "intends", "anticipates", "believes", "potential", "predict", "foresee", "proposed", "aim", "target", "opportunity", "could", "nominal", "conceptual" and similar expressions. Forward-looking statements, opinions and estimates included in this report are based on assumptions and contingencies which are subject to change without notice, as are statements about market and industry trends, which are based on interpretations of current market conditions. Forward-looking statements are provided as a general guide only and should not be relied on as a guarantee of future performance. Forward-looking statements may be affected by a range of variables that could cause actual results to differ from estimated or anticipated results and may cause the Company's actual performance and financial results in future periods to materially differ from any projections of future performance or results expressed or implied by such forward-looking statements. So, there can be no assurance that actual outcomes will not materially differ from these forward-looking statements.