Completion of Geophysical Surveys 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.

14 July 2025

Great Southern Copper plc

("GSC" or the "Company")

Gradient Array IP Anomaly Extends for 2.5km South of Mostaza Cu-Ag Mine

Results define high priority Phase III drill targets for potential extensions of Cu-Ag Mineralisation

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce the completion of ground geophysical surveys at the Cerro Negro prospect. Initial results from the Gradient Array induced polarisation (IP) survey define multiple geophysical targets along trend south of the mine.

Highlights:

· Geophysical surveys completed at Cerro Negro in advance of Phase III drilling

· Gradient array IP chargeability highs correlate closely with known Cu-Ag sulphide mineralisation intersected in previous GSC drilling1,2,3,4

· Chargeability anomalies correlate with low resistivity, indicative of hydrothermal alteration

· Results define a 2.5km long anomalous trend to the south of the Mostaza Cu-Ag mine which remains open

· The geophysical anomalies are coincident with anomalous surface rock chip geochemistry5

· Processing and interpretation of Pole-Dipole IP (PDIP) and Audio-frequency magneto-telluric (AMT) survey results are awaited

· Phase III drilling preparation is well advanced

· GSC holds option to own 100% of the Cerro Negro prospect, including the Mostaza mine

· Prospect located at low elevation with excellent access to infrastructure and mining services

· To prioritise Especularita, GSC will not proceed with the option agreements at the San Lorenzo Cu-Au and Monti Li projects

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "The preliminary results of the gradient array IP survey define a 2.5km long anomaly south of the Mostaza mine, which is consistent with the results of the Company's earlier rock sampling and mapping results.

"This is an exciting development and confirms significant potential for the Mostaza copper-silver mineralisation to extend southward along the Mostaza Fault Zone. We eagerly await the final results of the AMT and pole-dipole IP surveys, which will provide critical insights to support us in finalising plans for our Phase III exploration drilling at Cerro Negro.

"The exploration results across the Especularita project are both compelling and transformative, advancing the project significantly. As such, the Company has decided to prioritise its spending focus at Especularita and will not proceed further with its San Lorenzo and Monti projects. With capital raising conditions still challenging, this is considered to be the most effective solution for maximising the potential of this opportunity."

Geophysics Survey Details:

A total of 2.44 line-kilometres of Pole-Dipole and Gradient Array IP surveys were completed at the Cerro Negro prospect by Southern Rock Geophysics (SRG) of Santiago, Chile. AMT data was also acquired along the same survey lines. The survey consisted of five lines, each ranging from 440 to 600 metres (m) in length (see Figure 1). Lines 2, 3, 4 and 5 were oriented east-west, perpendicular to the primary north-south mineralisation trend. Line 1 was aligned northwest-southeast, targeting beneath the historic Mostaza Mine while avoiding stockpiled ore and pit walls. The survey was designed to identify the potential for the Mostaza-style Cu-Ag mineralisation to extend south of the open pit, where outcropping alteration and anomalous rock geochemistry define a structurally-controlled mineralised trend. Results will assist in defining Phase III drill targets along and adjacent to the Mostaza Fault that correlate with the known mineralised lenses identified by mapping and sampling5.

Preliminary results include plan maps for the Gradient Array IP. 2D inversion model sections and 3D inversion for the PDIP and AMT data are in process. Results are pending and will be integrated into the ongoing interpretation once available. Detailed interpretation by GSC and SRG, including the use of petrophysical properties testing of drillcore samples and predictive forward modelling, will be conducted once the full results are received.

Gradient Array IP Survey Results:

Gradient Array IP provides a 2D plan-view representation of electrical properties in the near surface. These include chargeability, which may indicate the presence of sulphide minerals and resistivity, which can reflect different rock types and their alteration.

At Cerro Negro, areas of high chargeability up to 12 milliseconds (see Figure 1) coincide with known mineralisation tested by drilling beneath the Mostaza Mine (Line 1) and the mineralisation intersected in hole DD007 (Line 2). In addition to these confirmed zones, the survey identified undrilled chargeability anomalies on Lines 3 and 4, located approximately 1km and 2km south of the mine, where previously reported surface rock-chip geochemistry returned highly anomalous values of Cu and Ag5.

Zones of low resistivity (see Figure 2) are spatially coincident with the chargeability highs, consistent with the presence of altered host rocks. Areas of high resistivity to the east and west of the central anomaly zone are interpreted to represent less altered, and hence more resistive lithologies.

Together, the chargeability and resistivity data define a coherent 2.5km-long anomaly consistent with the trend of the Mostaza Fault Zone, highlighting multiple high-priority targets for follow-up drilling.

The results suggest that further survey lines to the south and north may be considered for the future, as well as in-fill lines and extensions of existing lines further to the east, where mapping has identified anomalous Cu-Ag hosted in sub-parallel structures with evidence of artisanal mining.

Figure 1: Cerro Negro Prospect. Plan of gradient array results for chargeability (top) and apparent resistivity (bottom).

San Lorenzo Cu-Au and Monti Li Projects:

Given the recent success of the exploration work at Especularita and the strong outlook for future exploration programmes there, GSC has made a strategic decision to prioritise capital deployment to Especularita. As a result, the Company will not proceed with the San Lorenzo and Monti option agreements. GSC will continue to assess new exploration and business opportunities that are aligned with the Company's investment strategy both in Chile and further afield as and when such opportunities arise.

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 1375O (24 June 2025): Exceptional Drilling Results Continue at Mostaza

5. RNS 3120K (31 Oct 2024): Cerro Negro Exploration 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-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.