Cobre Limited has kicked off a major 40,000-metre drilling campaign at its Sierra Atacama copper project in Chile, aiming to convert its existing NI 43-101 resource to JORC compliance and explore opportunities for a larger open-pit operation.
- 40,000m surface and underground drilling underway
- Targeting JORC compliance for existing NI 43-101 resource
- Focus on expanding resource to support large-scale open-pit mining
- Starter pits planned for near-term production boost
- High-grade zones with precious metal credits under investigation
Major Drilling Campaign Targets JORC Upgrade and Resource Expansion
Cobre Limited (ASX:CBE) has commenced a substantial 40,000-metre drilling programme at its Sierra Atacama copper project in Chile, marking a pivotal step toward upgrading its resource to JORC standards and exploring the potential for a significantly larger-scale open-pit operation. The campaign comprises approximately 15,000 metres of reverse circulation drilling and 25,000 metres of diamond core drilling, conducted both from surface and underground.
This drilling initiative is designed to convert the current NI 43-101 resource estimate of around 110 million tonnes at 0.67% total copper; which is classified as a foreign estimate under Australian rules; to a JORC-compliant resource and reserve. This conversion is critical for Cobre to formally rely on the resource for development and investor reporting.
CEO Adam Wooldridge emphasised the strategic shift underway: "Transitioning from underground to open-pit mining has the potential to significantly increase operational scale in a manner better suited to the geometry of the mineralised system." The mineralisation outcrops at surface, and existing mining permits streamline the path toward staged expansion, starting with shallow starter pits and progressing to a larger open-pit operation leveraging current infrastructure.
Unlocking High-Grade Zones and Starter Pits for Early Production
A key focus of the drilling is delineating the high-grade mixed zone at the base of the oxide layer, where assays have shown copper grades exceeding 10% total copper, along with significant silver and gold credits. Recent underground samples from this zone returned remarkable grades such as 52.92% CuT with 148 g/t silver and 0.68 g/t gold, underscoring the potential economic sweetener this zone could provide.
Alongside targeting high-grade zones, the programme aims to identify near-term starter pits where copper lies close to surface, allowing for rapid and cost-effective extraction. These starter pits could supplement existing underground production while the larger-scale open-pit development is planned and permitted.
The drilling will also test underexplored gaps between known deposits, particularly between the Chabuca-Rebeca and Roxana trends, to confirm mineralisation continuity that could support a single, large open pit rather than multiple smaller operations. This approach could deliver significant economies of scale.
Existing Infrastructure and Parallel Validation Efforts
Sierra Atacama is an operating mine with established underground workings, a leaching processing plant, and good access to ports and roads near Antofagasta, a major Chilean mining hub. Cobre is conducting complementary work alongside drilling, including a high-resolution drone magnetic survey to map underground structures, detailed geological mapping to build a 3D model, and metallurgical test work aimed at improving copper recovery rates from oxide and transitional ores.
The company is also validating approximately 140 kilometres of historical drilling data and over 7,500 underground samples, addressing past inconsistencies in assay quality and incorporating modern QA/QC standards. This validation is essential to underpin the JORC resource upgrade and to inform future mine planning.
This drilling campaign follows Cobre's recent milestone to secure majority control of the Sierra Atacama project through a $60 million capital raise and staged acquisition strategy, which set the stage for operational control and long-term development plans Cobre Secures $60m to Take Control of Chile Copper Mine.
Exploration Upside Beyond Current Mining Area
The current mining footprint covers only a fraction of the total 10 km by 17 km property, which includes at least seven additional prospect areas with minimal modern exploration despite historical mining activity and visible copper outcrops. These prospects, along with largely unexplored southern exploration concessions bordering major deposits like Marimaca and Mantos Blancos, present significant longer-term upside potential.
While the initial focus remains on resource validation and expansion within the existing mining area, these broader lease areas could materially extend the mine life and resource base in future phases.
Bottom Line?
Cobre’s 40,000m drilling push is a critical test of Sierra Atacama’s scale and grade potential, with JORC conversion and open-pit expansion prospects hinging on upcoming assay results and validation work.
Questions in the middle?
- Will the drilling confirm continuity between known deposits to justify a large open-pit design?
- How extensive and economically viable is the high-grade mixed zone with precious metal credits?
- What improvements in metallurgical recovery can be achieved for oxide and transitional ores?