Cu-Ag Channel Results Confirm Scale of Monolith

Great Southern Copper PLC

22 July 2026

 

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.

22 July 2026

Great Southern Copper plc

("GSC" or the "Company")

Broad Cu-Ag Channel Results Confirm Scale of Monolith Zone and Define Drill Targets

Results significantly enhance potential global scale and prospectivity of Cerro Negro and the Mostaza discovery

Great Southern Copper plc (LSE: GSCU), the company focused on copper-gold-silver exploration in Chile, is pleased to report results from recent surface channel sampling at the Monolith Target, Cerro Negro Prospect, located just 400m to the southeast of the high-grade Mostaza Cu-Ag discovery and part of the Especularita Project.

Results from 20 channel traverses, representing 409 metres ("m") of sampled outcrop and 214 samples, confirm broad zones of highly anomalous copper-silver mineralisation associated with quartz veining within the silica-clay altered dacite dome.

Highlights:

·    All channel samples returned anomalous Cu-Ag across broad intervals. Key results include:

o  CH021-A: 56m @ 28.5 g/t Ag & 1,745 ppm Cu, including 6m @ 81.5 g/t Ag & 7,890 ppm Cu.

o  CH035-B: 56m @ 19.2 g/t Ag & 348 ppm Cu, including 14m @ 45.6 g/t Ag & 245 ppm Cu.

o  CH035-D: 24m @ 38.9 g/t Ag & 969 ppm Cu.

o  CH035-C: 10m @ 32.4 g/t Ag & 2,026 ppm Cu, including 2m @ 100.0 g/t Ag & 6,970 ppm Cu.

o  CH041: 78m @ 10.1 g/t Ag & 736 ppm Cu, including 12m @ 27.2 g/t Ag & 831 ppm Cu, and 12m @ 31.0 g/t Ag & 1,459 ppm Cu.

·    Anomalous channel and rock chip results define a zone of Cu-Ag mineralisation over an area of 700 x 400m

·    Mineralisation hosted in altered dacite dome rock and of similar type to the Mostaza deposit located 400m to the northwest

·    Surface leaching and oxidation processes have depleted the outcropping mineralisation suggesting potential for higher grades at depth

·    The results reinforce Monolith as a priority target and ready for drilling

·    Soil and ASD sampling is continuing across the Cerro Negro portion of the La Colorada lithocap

·    GSC holds rights to own 100% of the Cerro Negro prospect, including the Mostaza mine, located at low elevation with excellent access to infrastructure, and mining services and along trend of major copper deposits including Los Pelambres, Altar and El Pachon

Sam Garrett, Chief Executive Officer of Great Southern Copper, said: "These exciting results further demonstrate the scale potential at the Monolith target and significantly enhance the prospectivity of the Cerro Negro prospect and the Mostaza deposit specifically. The broad anomalous channel intervals confirm that mineralisation extends through extensive quartz-vein crackle and stockwork zones within the dacite dome.

"Despite being in the oxidised leached surface environment, intervals including 78 metres at 10.1 g/t silver and 736 ppm copper, and 56 metres at 28.5 g/t silver and 1,745 ppm copper, are highly anomalous when compared with background values of only 10-20 ppm copper and 0.05 g/t silver in the unmineralised and unaltered dacite, and suggest that higher grades are likely to occur at depth below the weathering profile.

"These results reinforce Monolith as a priority target within the Cerro Negro prospect as we continue to refine our geophysical interpretation and drill-targeting plans."

Cerro Negro Prospect:

The Especularita Project, including the Cerro Negro prospect and Monolith target, is located at low altitude within the Cretaceous-aged coastal metallogenic belt of northern Chile that includes large-scale copper mines and development projects including Carmen de Andacollo and El Espino (Figure 1). Significantly, the project is also located within a northwest-southeast trending structural lineament that links Especularita with notable large-scale porphyry Cu-Au mines and projects, including Los Pelambres, Altar-Piuquenes and El Pachon (Figure 1).

Figure 1: GSC's Especularita project is located at low altitude within the coastal metallogenic belt of northern Chile and within 50km radius of over 50Mt of contained copper metal defined in mines and advanced projects.

Monolith Cu-Ag Target:

Monolith is located approximately 400m southeast of the Mostaza Mine, within the Cerro Negro prospect (Figure 2). Previous mapping and sampling at Monolith defined a Cu-Ag mineralised and silica-clay altered footprint of approximately 700m by 400m¹.

Mineralisation is hosted by silica-clay altered dacitic to rhyodacitic, locally flow-banded volcanic rocks interpreted to form part of a resurgent dome complex. The hydrothermal system comprises an anastomosing network of quartz veinlets, crackle breccias stockworks and larger quartz-baryte veins developed within broad zones of silica-clay alteration (Figure 3).

Copper oxides occur on fractures and within quartz-veinlet networks, while limonite-goethite boxworks and the strongly oxidised character of the outcrop indicate extensive weathering and leaching of primary sulphides near surface.

Figure 2: Monolith target, Cerro Negro. Silver (left) and copper (right) assay results for new and previously reported samples.

Figure 3: Broad mineralised zone exposed across the Monolith ridge (left) and visible copper oxides associated with quartz-vein stockwork and crackle veining in altered dacite (right)

Channel Sampling Results:

A total of 20 channel traverses, comprising 214 channel-chip samples collected generally over 1-2m intervals, were completed across the Monolith target for a combined sampled length of 409m. The programme was designed to test the continuity and distribution of Cu-Ag mineralisation associated with the silica-clay altered dacite dome. Where practicable the channel samples were collected across the strike of the outcropping mineralisation (Figure 4).

All channel samples returned anomalous Cu-Ag across broad intervals. The longest channel composite CH041 returned;

·    78m @ 10.1 g/t Ag and 736 ppm Cu

o  Including 12m @ 27.2 g/t Ag and 831 ppm Cu

o  And 12m @ 31.0 g/t Ag and 1,459 ppm Cu

CH021-A returned;

·    56m @ 28.5 g/t Ag and 1,745 ppm Cu

o  Including 40m @ 39.2 g/t Ag and 2,174 ppm Cu

o  Including 6m @ 81.5 g/t Ag and 7,890 ppm Cu

CH035 channels (CH035 A-D) also returned broad and consistent anomalism, including;

·    CH035-B: 56m @ 19.2 g/t Ag and 348 ppm Cu

·    CH035-C: 10m @ 32.4 g/t Ag and 2,026 ppm Cu

·    CH035-D: 24m @ 38.9 g/t Ag and 969 ppm Cu

o  Including 2m @ 100.0 g/t Ag and 6,970 ppm Cu

Barren, unaltered and unmineralized dacite host rock at Monolith has background Cu-Ag assay grades of approximately 10-20 ppm Cu and 0.05 g/t Ag. The new channel composites therefore represent copper values from multiples to several hundred times background, and silver values more than two orders of magnitude above background. This is considered highly significant in the strongly oxidised and leached surface environment and suggests potential for higher grades in the sulphide zone at depth below the weathering profile. A summary of significant Cu-Ag channel intervals is given below in Table 1.

Portions of CH021 were previously disclosed as individual 1-2m channel-chip results in RNS 1932D dated 14 October 2025 and were displayed as point results because short breaks in the original channel prevented a continuous composite². Additional infill channel-chip samples have since been collected and assayed to close those breaks. Previously disclosed assays are included in the composite but are not new results, and no unsampled intervals have been assigned a grade.

Next Steps:

The results will be integrated with detailed geological mapping, structural interpretation and geophysical data to update the Monolith geological model and refine drill targeting. Follow-up work will focus on the continuity of the broad crackle-stockwork zones and extensions of the mineralised system to the south and west. Additional geophysical surveys are being planned to help refine drill targets prior to scout drill testing.

Figure 4: Detailed Monolith channel-sampling map showing selected broad Cu-Ag channel composites. Channel lengths are measured along surface outcrop; true widths are not known.

Channel ID		From (m)	To (m)	Interval (m)	Cu (ppm)	Ag (g/t)
CH018		4	13	9	700	6.2
	incl.	4	6	2	1,118	1.3
CH021-A		0	56	56	1,745	28.5
	incl.	16	56	40	2,174	39.2
	incl.	48	54	6	7,890	81.5
CH021-B		0	4	4	355	7.6
CH021-C		0	10	10	2,057	27.5
	incl.	2	4	2	6,970	100.0
CH035-B		0	56	56	348	19.2
	incl.	0	14	14	245	45.6
CH035-C		0	10	10	2,026	32.4
	incl.	0	4	4	3,795	41.9
CH035-D		0	24	24	969	38.9
CH037		0	14	14	2,087	29.8
CH039-A		0	2	2	1,010	38.3
CH040-B		0	4	4	131	22.3
CH041		0	78	78	736	10.1
	incl.	0	12	12	831	27.2
	and	38	50	12	1,459	31.0
CH042		0	2	2	4,420	49.1

Table 1: Significant results from Monolith channel samples in this release.

Sampling, Assaying and Data Aggregation:

Channel samples were collected as continuous chip samples, generally over 1-2m intervals, across exposed bedrock. Sample locations were recorded using hand-held GPS units in WGS84 / UTM Zone 19S and each sample was assigned a unique ticket-book identifier. Samples were transported by Company personnel to ALS Laboratories in Santiago, Chile, for weighing, drying, crushing and pulverising. A 200g pulp split was forwarded to ALS Lima, Peru, for gold assay by 30g fire assay with ICP-AES finish (ALS method Au-ICP21) and multi-element analysis by four-acid digest and ICP-MS (ALS method ME-MS61).

References:

1.    RNS 7344A (16^th April 2026): Mineralisation Extended at Monolith Target

2.    RNS 1932D (14^th October 2025): High Grade Ag-Cu Samples Expands Monolith Target

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/

Enquiries:

Great Southern Copper plc	https://gscplc.com/link/Pqd6nr
Sam Garrett, Chief Executive Officer	[phone]
SI Capital Limited
Nick Emerson	[phone]
BlytheRay
Tim Blythe / Megan Ray	[phone] [e-mail]

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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

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.

 

END