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.

17 March 2025

Great Southern Copper plc

("GSC" or the "Company")

"Exceptional" High-Grade Cu-Ag Results Confirm Potential of the Mostaza Deposit, Cerro Negro

Assays demonstrate continuity of grade with mineralisation open laterally and at depth

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to report further exceptional assay results from Phase I drilling at the Mostaza Mine, Cerro Negro.

Highlights:

·    Assay results received for holes CNG25 DD002 - DD005 with significant intervals including;

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

§   7.0m of 5.08% Cu and 449.6 g/t Ag from 45m, within a broader zone of

§ 21.0m of 2.88% Cu and 246.7 g/t Ag from 35m

Ø DD003:  13.0m of 2.48% Cu and 198.1 g/t Ag from 39m, within a broader zone of

§ 18.6m of 1.85% Cu and 146.6 g/t Ag from 36.6m

Ø DD002:   4.2m of 1.73% Cu and 126.5 g/t Ag from 38.9m

·    New results demonstrate continuity of high grades building upon earlier reported assays for hole CNG25 DD001¹;

Ø DD001:  20.0m of 3.31% Cu and 269.9 g/t Ag from 27m, including

§   7.0m of 5.72% Cu and 489.6 g/t Ag from 31m

·    Assay grades consistently significantly higher than reported results of historical drill program

·    Mineralisation remains open in all directions

·    Assay results for remaining Phase I drill holes, CNG25 DD006 - 009, are pending

·    Phase II diamond drilling in progress aiming to expand on historically reported resources and test exploration targets²

·    GSC holds option to own 100% of the Mostaza mine and Cerro Negro project

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

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "These outstanding results confirm that high grade Cu-Ag mineralisation is continuing to depth and along strike and demonstrate that the former Mostaza mine has the potential to be a high-grade high-value Cu-Ag deposit.

"Two diamond drill rigs are now on site - one targeting strike and depth extensions of the Mostaza pit mineralisation and a second rig is exploring the structural trend to the south following up earlier drilling of holes DD006-009.

"We have entered a very exciting phase of exploration at Cerro Negro and have a lot of work to do as we progress to demonstrate the potential economic viability of this exciting deposit."

Results of diamond drillholes CNG25 DD002 - DD005

Diamond drillholes CNG25 DD002 - DD005 were designed to target shallow extensions of the historical Mostaza Lens 2 mineralisation at depth and along strike of the intercept in CNG25 DD001 (Figure 1). Due to access and safety limitations in the old mine pit the five holes were drilled in a fan pattern from a centrally located drill pad and were planned to intersect the mineralised body on an approximate grid pattern.

All holes intersected the Lens 2 mineralised body over varying widths and significant assays are summarised in Table 1. The mineralisation is also weakly anomalous in Sb-As and exhibits pathfinder anomalism for Bi-Cd-Li-Zn which is consistent with the high-sulphidation style of mineralisation.

Drillhole CNG25 DD002 was drilled to intersect the lens approximately 25m north of hole DD001 and returned 4.2m @ 1.73 % Cu, 126.5 g/t Ag, and 0.0824 % Sb from 38.9m. CNG25 DD003, which was designed to test the lens below hole DD002, intersected 18.6m @ 1.85% Cu, 146.58 g/t Ag from 36.6m, including 13m @ 2.48 % Cu, 198.09 g/t Ag from 39m, with maximum grades of 1m @ 4.64 % Cu, 406.00 g/t Ag, and 0.22% Sb from 50m. These results appear to demonstrate that both Cu-Ag grade and thickness the lode is increasing with depth.

Hole CNG25 DD005 was drilled below hole DD001 and intersected broad intervals of high-grade Cu-Ag similar to mineralisation seen in hole DD001¹ including 7m @ 5.08 % Cu, 449.57 g/t Ag from 45m, and 2m @ 6.05 % Cu within a broader lens-wide zone of 21m @ 2.89 % Cu, 246.71 g/t Ag from 35m.. Maximum grades of 6.2 % Cu, 567 g/t Ag, and 0.23 % Sb are reported over 1m.

Hole CNG DD004 was drilled to the north of DD002 and intersected only weakly altered and mineralised "proto-lens" in a zone of faults and dykes where the lens was otherwise expected, suggesting the lode has been structurally displaced or "pinched out" in this location.

A summary of all Phase I assay results to date are shown in Table 1 below.

Table 1: Summary of significant intercepts for Phase I GSC drill holes.

The Mostaza Cu-Ag deposit, Cerro Negro

The high-grade Cu-Ag mineralisation at Mostaza is confined to a north-south trending, structurally-controlled lode, or "lens" (specifically Lens 2), of variable width (<4-20m) that dips moderately steeply to the west (Figure 2). Copper mineralisation comprises abundant disseminations, veinlets, crackle networks, and breccia matrix fillings of hypogene black to dark metallic grey chalcocite with lesser bluish bornite and traces of chalcopyrite and pyrite (Figure 3). Petrographic confirmation is pending, however, the copper mineralogy may include other silver-rich copper minerals such as stromeyerite (AgCuS) for example.

Lens 2 host rocks are intensely altered and appear to comprise multiple generations of breccia, tuffisite, and felsic intrusive altered to texturally destructive illite ± montmorillonite overprinted by probable alunite ± dickite ± pyrophyllite (to be confirmed by petrographic studies). The high-grade Cu-Ag mineralised lens exhibits sharp contacts and is bounded to the east and west by faults that are typically invaded by narrow (<1-2m) andesite to rhyolite dykes. Outside of the bounding dykes and faults, the enclosing wall rocks consist of an east-dipping bedded sequence of fresh, black volcanic lava flows and red, hematite-rich phreatic and/or phreatomagmatic breccias that might be part of a large dome-diatreme complex outcropping to the east.

Insufficient drilling is available to date to allow detailed interpretation of the architecture of the deposit. The lack of high-grade mineralisation intersected in hole DD004 indicates late-stage structural dislocation occurs resulting in variable localised thinning or boudenaging of the lenses. Broad zones of weakly anomalous silver (>0.1ppm Ag) in hole DD004 might also suggests the potential for this hole to be adjacent to significant lode mineralisation. The narrower lode width intersected in hole DD002 suggests also that mineralisation may be "stoped out" in places by post-mineral dykes of the same type that intrude the bounding fault structures.

The high-grade Cu-Ag mineralogy type and associated advanced argillic style alteration suggests the lodes at Mostaza are part of a high-sulphidation epithermal system, potentially related to a yet-to-be-discovered porphyry style deposit occurring at depth.

The Lens 2 mineralisation is interpreted to form one of a number of Cu-Ag rich bodies mapped at surface which have historically been interpreted as discrete "lenses" but which collectively have the potential to make up an anastomosing network of structurally controlled zones of mineralisation continuous over a strike length of greater than 1-2km.

The results of CNG25 DD001- DD005 targeting mineralisation beneath the existing Mostaza open pit demonstrate that the deposit continues at depth and along strike from the historical drilling and is open in all directions (Figure 4).

Figure 1: Cerro Negro Project, Mostaza Mine: Simplified schematic long section of Lens 2 with circles showing the approximate location of where Phase 1 drillholes intersect the hanging wall of the mineralised lens. The apparent thickness of copper mineralisation is indicated below each intersection point. Note that mineralisation remains open at depth and along strike. Historical resource blocks are for reference.

Figure 2: Cerro Negro Project, Mostaza Mine: Schematic cross section through drillholes CNG25 DD001 and DD005 showing Cu-Ag intercepts and the preliminary geological interpretation and relationship to historical drillholes. Note the extrapolations from diamond holes DD001 and DD005 to the historical drillholes EDH25, 23 and 15 are based on assay results only because historical drill core and logs are unavailable.

Figure 3: Cerro Negro Project, Mostaza Mine. Photograph of core from hole CNG25 DD002 and DD003, on the left, and DD005 on the right, with grades of Cu % and Ag g/t. The black disseminations, veinlets and crackle fill are Cu-Ag bearing sulphides and sulfosalt minerals in association with minor silica and baryte gangue cutting clay-rich alteration.

Core preparation, sampling and assaying

The Mostaza diamond drill core is collected from site by GSC staff and transported to the Company's nearby sampling facilities where it is then processed for geological, geotechnical, petrophysical and geochemical data. Sampling intervals are selected principally on geologic boundaries and may vary in length up to 2m. The core is cut into two halves using an electric diamond brick saw with half-core samples each allocated a unique identifier code and bagged-tagged separately. Samples for each complete hole are transported by GSC personnel to ALS laboratories in Santiago, Chile for sample preparation (drying, weighing, crushing and grinding). A final 200g aliquot of each sample is forwarded by ALS to their laboratories in Lima, Peru where it is assayed for Au (by 30g fire assay with ICP-AES finish method) plus a suite of 48 base metals and trace elements including Cu and Mo (by four acid digest ICP-MS method).

Sampling and assaying QAQC protocols employed by the company for this drilling project include routine insertion of standard reference materials including standards and blanks. Results for each SRM is assessed to monitor the accuracy and precision of the assay data from ALS for the core samples.

Next steps

Phase II diamond drilling at Mostaza has commenced and is designed to include resource and exploration drilling. Metallurgical studies of drill core, stockpiles and tailings are also being planned. Extensions of mineralisation at depth and along trend under cover may also be targeted with geophysical surveys.

Table 2: Cerro Negro Project, Mostaza Mine; Mostaza drill core assay results for Cu, Ag and Sb.

Cautionary note:

The Company cautions that all references to "resources", "mineral resources", or "mineral resource estimates" in this RNS are historical and were prepared and reported prior to the implementation of the JORC code and therefore are non-JORC compliant. The Company advises that the resource categories used in the historical estimates, for example "measured, indicated, demonstrated and inferred", may not have the same meaning or degree of confidence as current JORC categories. Historical records indicate that the quoted non-JORC resources were calculated using the polygonal method based on underground sampling, 1024m of drilling in 25 holes, and geological cross-sections and level plans. GSC is presenting this information for historical context only and is not treating it as a current mineral resource estimate. The Company has not been able to independently verify the results of historical drilling or mine channel samples. References to mineralised grade intervals in drill holes are considered apparent thicknesses as there is not sufficient geological information to calculate true thickness of mineralised intercepts at this time.

References:

1.       RNS 5182Y (26 February 2025): Cerro Negro assays return 20m of3.3% Cu & 270g_t Ag

2.       RNS 2017A (11 March 2025): Phase II Resource Drilling Commences at the Mostaza Cu-Ag Deposit

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 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 copper producer and the second-largest producer of lithium.

The two early-stage Cu-Au projects comprise the 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.

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 deposits as well as high-grade Cu-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.