Highlights

  • Third drill rig mobilised to expand Phase III drilling at Cerro Negro.
  • Scout RC drilling to test MFZ and newly mapped hanging wall mineralisation.
  • Rock chip sampling returns up to 2.56% Cu and 293 g/t Ag across 1.5km trend.

Great Southern Copper plc (LSE:GSCU) has initiated an expansion of its Phase III drilling programme at the Cerro Negro prospect within the Especularita Project in Chile. A third drill rig is being mobilised to begin scout reverse circulation (RC) drilling across key targets along the Mostaza Fault Zone (MFZ) and within the hanging wall volcanics, where recent mapping has identified new oxide copper occurrences.

The updated programme is designed to advance the assessment of multiple high-priority targets identified through geological mapping, geochemical sampling, and geophysical surveys across the Mostaza trend.

Focus on Mostaza Fault Zone Targets

Initial scout RC drilling, totalling up to 1,000m, will evaluate a series of outcropping silicified lenses along the southern extension of the MFZ, situated approximately 1–1.5km south of the historic Mostaza Mine. These lenses exhibit strong silica alteration, crackle brecciation and boxwork textures, reflecting features observed across other surface-leached mineralised zones at Cerro Negro.

Sampling from leached silicification has reported assays up to 86.4 g/t Ag, accompanied by anomalous Mo, Cu, As and Sb. These results align geochemically with signatures associated with high-grade material documented at the Mostaza Mine. Due to intense leaching in near-surface environments, copper grades at outcrop remain subdued but are interpreted as representing the weathered upper portions of mineralised lenses. The MFZ targets also correspond to IP chargeability and conductivity anomalies mapped along the structural trend.

Newly Identified Hanging Wall Mineralisation

A further 1,000m of RC drilling will test recently mapped oxide copper mineralisation within the west-side hanging wall of the MFZ. Although surface exposure is limited by gravel and talus cover from the adjacent dacite dome, several outcropping windows of brecciated andesite with visible oxide copper have been identified and sampled across a 1.5km trend extending south of the mine.

Assays from 22 rock chip samples collected in this area returned grades up to 2.56% Cu and 293 g/t Ag. Within the set, 45% of samples were anomalous for Cu (>0.1% Cu) and 68% for Ag (>5 g/t Ag). The distribution and grades suggest the presence of leached oxide copper near surface, supporting the potential for shallow targets to be evaluated through drilling.

Progress on Phase III Diamond Drilling

Parallel to the RC programme, two diamond drill rigs continue operating at Cerro Negro, targeting extensions to the Cu-Ag mineralisation beneath the Mostaza open pit and in the Lens 3–5 zone. As of late October 2025, 1,340m of diamond drilling across 10 holes has been completed, with 572 samples dispatched for laboratory analysis. Geological logging and modelling of the Mostaza deposit are ongoing.

Current drilling includes a re-drill of hole CNG25-DD033, which encountered multiple mineralised lenses before terminating early due to rig malfunction at 197.9m in chalcocite-bearing breccia. The twin hole aims to test the full width of this deeper mineralised lens, while additional drilling beneath Lens 5 is continuing to define subsurface extensions of silicified and brecciated dacite hosting oxide copper.

Share Performance of GSCU

GSCU was trading 1.95% higher at GBX 2.75 per share as of 11 November 2025 at the time of writing.