£2m Raised to Advance Mostaza Towards Resource

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.

8 October 2026

Great Southern Copper plc

(“GSC” or the “Company”)

GSC secures £2m funding to advance high grade Mostaza towards resource definition

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to announce that it has raised £2 million to finance the ongoing exploration programme at its high-grade Mostaza copper-silver discovery and other selected targets within its Especularita Project through a placing of new equity (the “Fundraising”).

£2.0 million raised through a private placing with existing and new investors ("Placing"), comprising the issue of 133,333,333 new ordinary shares (the “New Shares”) at a placing price of 1.5 pence per share, being a 6 per cent. discount to the Company’s previous days closing share price. The New Shares represent approximately 15 per cent. of the Company’s enlarged issued share capital.

As part of the Placing, the Company’s Directors intend to subscribe for 4,666,667 shares for total proceeds of £70,000.

The Placing is conditional on admission of the New Shares to the Equity shares (transition) category of the Official List of the Financial Conduct Authority (“FCA”) and to trading on the Main Market of the London Stock Exchange becoming effective (“Admission”).

Rationale for Fundraising and Use of Proceeds

In recent months, the Company has made significant progress at its Mostaza project, with drilling demonstrating the continuity of high-grade copper-silver mineralisation along strike and at depth. Exploration at the nearby Monolith target has further enhanced the potential scale of the mineralised system within the wider Cerro Negro prospect, while preliminary metallurgical test-work on high-grade Mostaza samples has delivered encouraging copper and silver recoveries using conventional flotation.

This funding will support the next phase of exploration, with the principal objective of advancing Mostaza towards a maiden mineral resource. The planned Phase IV drill programme comprises up to 5,000 metres of diamond drilling at Mostaza and Monolith, together with up to 2,000 metres of reverse circulation (“RC”) drilling along the Mostaza Fault trend, to further assess the extent and continuity of mineralisation. Phase II metallurgical test-work will build on the initial results through testing drill-core samples across a broader range of copper-silver grades.

In addition, the proceeds will support 1,000 metres of RC drilling at the Artemisa porphyry prospect and provide for corporate costs and general working capital. Subject to available funding, the Company intends to undertake further drilling and technical studies at Artemisa, with the scope of any programme prioritised according to exploration results and the objective of progressing Mostaza towards resource definition.

Sam Garrett, Chief Executive Officer of Great Southern Copper plc, said:

“This funding will allow us to build on the progress made at Mostaza and advance the discovery towards a maiden resource. Our drilling has demonstrated the continuity of high-grade copper-silver mineralisation, while the encouraging initial metallurgical results provide further confidence as we plan the next phase of work.

“The programme will focus on further drilling at Mostaza, testing the nearby Monolith target and investigating mineralisation along the Mostaza fault trend. Alongside this, further metallurgical testing will help us better understand the deposit as we continue to assess its potential.

“We also look forward to advancing exploration at Artemisa our exciting porphyry target, while maintaining Mostaza as our principal priority. We greatly appreciate the ongoing support of our investors and look forward to updating the market as this work progresses.”

Admission and Total Voting Rights

Application will be made for the 133,333,333 New Shares, which will rank pari passu in all respects with the existing ordinary shares in the Company, to be admitted to listing on the Equity shares (transition) category of the Official List of the FCA and to trading on the Main Market of the London Stock Exchange plc, which is expected to occur at 8.00 a.m. on or around 15 October 2026.

Following Admission of the New Shares, the total number of ordinary shares and voting rights in the Company will be 906,703,489. This figure may be used by shareholders in the Company as the denominator for the calculations by which they will determine if they are required to notify their interest in, or a change to their interest in, the share capital of the Company under the FCA's Disclosure and Transparency Rules.

Enquiries:

Engage with the GSC management team directly by asking questions, watching video summaries and seeing what other shareholders have to say. Navigate to our Interactive Investor hub here: https://gscplc.com/

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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