Geophysics Surveys Commence at Cerro Negro

THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION AS STIPULATED UNDER THE UK VERSION OF THE MARKET ABUSE REGULATION NO 596/2014 WHICH IS PART OF ENGLISH LAW BY VIRTUE OF THE EUROPEAN (WITHDRAWAL) ACT 2018, AS AMENDED. ON PUBLICATION OF THIS ANNOUNCEMENT VIA A REGULATORY INFORMATION SERVICE, THIS INFORMATION IS CONSIDERED TO BE IN THE PUBLIC DOMAIN.

5 June 2025

Great Southern Copper plc

("GSC" or the "Company")

Geophysics Surveys Commence at Cerro Negro Prospect, Especularita Project

IP and AMT surveys to target extensions of high-grade Cu-Ag mineralisation at Mostaza

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold exploration in Chile, is pleased to announce that it has commenced pole-dipole induced polarisation (PDIP) and audio frequency magneto-telluric (AMT) geophysics surveys on the Cerro Negro prospect at the Company's Especularita Project in Chile.

Highlights:

· Exploration geophysics surveys commence at Cerro Negro prospect

· Four lines of PDIP and AMT surveys to detect potential extensions of high-grade Cu-Ag mineralisation below and along trend of the Mostaza mine

· Survey results to assist in targeting Phase III exploration drilling at Cerro Negro up to two kilometres south of the Mostaza mine where Phase I drilling intersected significant Cu-Ag mineralisation including:

Ø 1CNG25-DD001: 20.0m of 3.31% Cu, 269.89g/t Ag from 27m

Ø 2CNG25-DD005: 12.0m of 4.24% Cu, 369.5 g/t Ag from 40m, and

Ø 3CNG25-DD007: 33m of 1.96% Cu and 60.6 g/t Ag from 87m

· Phase II drilling results for holes CNG25-DD010 to CNG25-DD025 are pending

· GSC holds options to 100% of the prospects that make up its Especularita Project

· Excellent access to national infrastructure including roads, power, port and townships

Sam Garrett, CEO for Great Southern Copper, said: "These important geophysical surveys will play a critical role in guiding our Phase III exploration drilling at Cerro Negro. Phases I and II relied on surface exploration results and we now want to explore deeper, both beneath the known mineralisation at Mostaza and along trend to the south.

"The IP survey is designed to detect the disseminated Mostaza-style sulphide mineralisation and resistivity contrasts of altered rocks down to some 200m depth. The AMT survey is run in parallel and provides resistivity data down to many hundreds of metres depth. The four survey lines will test a two kilometre strike length of the Mostaza mineralised system, however, mineralisation remains open still further to the south.

"We look forward to announcing the results of these surveys as well as the drilling results for Mostaza and Viuda Negra."

Geophysics surveys, Cerro Negro:

The Company has contracted Southern Rock Geophysics (SRG) of Santiago, Chile to complete four initial pole-dipole induced polarisation (PDIP) and coincident audio frequency magnetotelluric (AMT) survey lines across the Mostaza trend (see Figure 1) at Cerro Negro. The PDIP will detect variations in electrical chargeability expected of the disseminated and crackle hosted sulphide mineralisation and resistivity variations expected of the altered lodes down to some 200 metres (m). AMT will detect variations in resistivity to several hundred metres depth.

Line 1 is designed to cross the Mostaza Mine area to test the depth extension of west dipping and subvertical high-grade Cu-Ag mineralisation reported in the following holes:

· 1CNG25 DD001: 20m @ 3.31 % Cu, 269.89 g/t Ag from 27m

o  Including 7m @ 5.72 % Cu, 489.57 g/t Ag from 31m

o  Including 3m @ 6.62 % Cu, 562.67 g/t Ag from 35m

· 2CNG25 DD003: 18.6m @1.85 % Cu, 146.58 g/t Ag from 36.6m

o  including 13m @ 2.48 % Cu, 198.09 g/t Ag from 39m

o  including 1m @ 4.64 % Cu, 406.00 g/t Ag, from 50m

· 2CNG25 DD005: 21m @ 2.89 % Cu, 246.71 g/t Ag from 35m

o  including 7m @ 5.08 % Cu, 449.57 g/t Ag from 45m

o  including 2m @ 6.05 % Cu, 547.50 g/t Ag from 45m

Line 2 will test the depth extent of mineralisation in Lenses 3, 4 and 5 which included the following drill results:

· 3CNG25 DD007: 33m @ 1.96% Cu and 60.6 g/t Ag from 87m

o  Including 3.85m @ 5.21% Cu and 318.2 g/t Ag from 88m, and

o  Including 2.5m @ 9.67% Cu and 175.4 g/t Ag from 116.4m

Lines 3 and 4 will test across undrilled outcrops along trend to the south, where mapping has identified altered and mineralised rocks that return assay grades up to 4.64% Cu and 177ppm Ag in rock grab and channel samples4.

Figure 1. Plan view of the Cerro Negro Prospect, showing the Mostaza Mine and the southward extension of observed alteration and mineralisation (red) to be investigated by the PDIP and AMT survey lines (yellow). Mineralisation remains open further to the south of Line 4. North to the right.

References:

1. RNS 5182Y (26 Feb 2025): Cerro Negro assays return 20m of 3.3% Cu, 270g/t Ag

2. RNS 9022A (17 Mar 2025): Exceptional results confirm potential of Mostaza

3. RNS 8896D (07 Apr 2025): Further exceptional assay results from Mostaza

4. RNS 3120K (31 Oct 2024): Cerro Negro Results Up To 4.64% Cu and 177ppm Ag

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 deposits in Chile. The Company has the option to acquire rights to 100% of two projects in the under-explored coastal belt of Chile that are prospective for large scale copper-gold deposits. Chile is a globally significant mining jurisdiction being the world's largest producer and exporter of copper.

The two, early-stage Cu-Au projects comprise Especularita and San Lorenzo Projects, both 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 both exploration project areas. 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.