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Great Southern Copper Reports Channel Sampling Results at Monolith Target Cerro Negro Prospect
Great Southern Copper plc reported 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 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. All channel samples returned anomalous Cu-Ag across broad intervals. Key results include: CH021-A: 56m @ 28.5 g/t Ag & 1,745 ppm Cu, including 6m @ 81.5 g/t Ag & 7,890 ppm Cu. CH035-B: 56m @ 19.2 g/t Ag & 348 ppm Cu, including 14m @ 45.6 g/t Ag & 245 ppm Cu. CH035-D: 24m @ 38.9 g/t Ag & 969 ppm Cu. CH035-C: 10m @ 32.4 g/t Ag & 2,026 ppm Cu, including 2m @ 100.0 g/t Ag & 6,970 ppm Cu. 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. 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. 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. Monolith is located approximately 400m southeast of the Mostaza Mine, within the Cerro Negro prospect. Previous mapping and sampling at Monolith defined a Cu-Ag mineralised and silica-clay altered footprint of approximately 700m by 400m. 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. 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. 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. 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 including 12m @ 27.2 g/t Ag and 831 ppm Cu 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 including 40m @ 39.2 g/t Ag and 2,174 ppm Cu 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 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 composite. 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. 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. Channel ID From (m) To (m) Interval (m) Cu (ppm) Ag (g/t) CH018 41 39 7 006.2 incl. 46 21,118 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 44 35 57.6 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 22 21,010 38.3 CH040-B 0 44 13 122.3 CH041 0 78 78 736 10.1 incl. 0 12 12 831 27.2 and 38 50 12 1,459 31.0 CH042 0 22 4,420 49.1. 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).
