By: Salini Krishnan
Aris Mining is moving Marmato into a new operating phase in Colombia, with underground development, a new Sandvik fleet, and a larger processing circuit all aligned around a step change in mining method. The expansion is designed to shift the operation from its long-running narrow vein model into the wider Bulk Mining Zone below the current workings, supported by a new 5,000 tonne-per-day carbon-in-pulp (CIP) plant.
The project matters because it changes Marmato from a smaller, selective underground producer into a more mechanised bulk mining operation with materially higher throughput. If commissioning and ramp-up stay on schedule, Aris is targeting annual gold production of about 200,000 ounces from Marmato, making it one of the more significant underground gold expansions under way in Colombia.
Marmato expansion: what is changing
The technical centrepiece of the expansion is the move beneath the existing Narrow Vein Mine into the Bulk Mining Zone, where mineralisation is wider and better suited to mechanised underground extraction. That shift requires a different mine layout, larger development headings, a higher-capacity haulage system, and a fleet designed for sustained underground production rather than highly selective narrow-width stoping.
Aris has paired that mine redesign with a new process plant. The 5,000 tpd CIP circuit is intended to replace the older flotation-based configuration and give the operation a flowsheet better matched to larger ore volumes and conventional whole-ore gold recovery. In practical terms, the mine plan and plant design are being advanced together: more bulk tonnes from underground only create value if surface processing can absorb them at stable recoveries.
Sandvik fleet delivery and underground mining implications
A key part of that transition is the delivery of new Sandvik underground equipment. Public disclosures around the order indicate the package includes loaders, underground trucks, and drill rigs for both mine development and production, together with maintenance support. Sandvik said the order was valued at about SEK250 million, with deliveries scheduled from the second quarter of 2026 through the second quarter of 2027.
For Marmato, fleet selection is not a procurement footnote; it is a direct enabler of the mining method. Loaders and trucks support higher daily material movement from larger stopes and development drives, while modern drill rigs improve advance rates, drilling accuracy, and cycle consistency. A standardised equipment fleet can also reduce maintenance complexity, improve parts availability, and support operator training as the operation scales up.
Industry reports on the package have referenced Sandvik units including development and production drills, underground haul trucks, and loaders suitable for mechanised stoping environments. That matters because the Bulk Mining Zone will depend on reliable drill-and-blast execution, disciplined ore handling, and consistent underground logistics if the project is to reach nameplate throughput.
From narrow vein mining to the Bulk Mining Zone
The biggest technical change at Marmato is the move away from narrow vein mining as the dominant production source. Narrow vein operations typically prioritise selectivity, tighter dilution control, and smaller mining geometries. They can be effective in higher-grade settings, but they are also constrained in scale and often harder to mechanise efficiently.
Bulk mining in a wider porphyry-hosted zone changes those trade-offs. The operating model becomes more dependent on development access, stope sequencing, ground support discipline, ventilation planning, paste or backfill strategy where applicable, and haulage efficiency. Dilution management remains critical, but the economic driver shifts toward achieving stable tonnage at acceptable grade and recovery rather than maximising selectivity tonne by tonne.
At Marmato, that shift should allow Aris to increase mining rates materially relative to the historical operation. It also introduces execution risk. Bulk underground mining demands strong geotechnical control, reliable development performance, and a processing plant capable of handling variable ore characteristics during ramp-up. In other words, the expansion is not simply a scale-up of the old mine; it is a transition to a different operating system.
5,000 tpd CIP plant and process route
The new 5,000 tpd CIP plant is central to the production target. CIP offers a proven route for gold recovery at this scale and is generally better suited than the legacy configuration for a mine plan built around higher tonnage from bulk underground stopes. The plant will need to deliver steady availability and recoveries as mine feed transitions from the current mining areas into the new Bulk Mining Zone.
Aris has indicated that the new circuit is expected to enter service in the fourth quarter of 2026, with ramp-up continuing thereafter. That timeline is important because underground mine development, fleet deployment, and plant commissioning must remain closely synchronised. If underground tonnage builds ahead of plant readiness, stockpiling and working capital pressure can rise. If the plant is ready before mining rates are established, the operation can face underutilised installed capacity.
Marmato expansion snapshot
| Component | Current/Legacy Position | Expansion Position |
|---|---|---|
| Mining method | Narrow vein underground mining | Mechanised bulk mining in the Bulk Mining Zone |
| Mobile fleet | Legacy mixed fleet | New Sandvik loaders, trucks, and drills |
| Process plant | Older flotation-based configuration | New 5,000 tpd CIP plant |
| Production profile | Smaller-scale output | Targeting ~200,000 oz/y gold |
| Ramp-up focus | Selective mining continuity | Integrated mine-and-mill scale-up |
Timeline and execution checkpoints
The near-term execution story at Marmato is straightforward: complete underground access and development into the Bulk Mining Zone, receive and deploy the Sandvik fleet, commission the CIP plant, and then ramp both systems together. Each milestone has technical significance.
Underground access determines whether stoping areas can be prepared on schedule. Fleet delivery affects development rates and materials movement. Plant commissioning determines whether the project can convert mined tonnes into saleable ounces at the expected pace. Because all three streams are interdependent, delays in one area can flow quickly into the others.
For operators and investors following the project, the most useful checkpoints over the next several quarters are likely to be development metres achieved, evidence of sustained mechanised mining rates, commissioning progress at the plant, and early operating indicators such as throughput, recoveries, and equipment availability.
Key risks to watch
The project’s upside is clear, but so are the technical risks. First is underground development risk: if access to the Bulk Mining Zone lags, production ramp-up may slip regardless of plant readiness. Second is commissioning risk at the CIP plant, especially during the early transition from construction to stable commercial operation. Third is mining dilution and grade control risk, which often become more visible when operations move from selective extraction to bulk stoping.
A fourth risk is integration. Marmato is not only adding new equipment and a new plant; it is changing mining philosophy, production cadence, and maintenance requirements at the same time. That raises the importance of operator training, maintenance planning, spare parts support, and short-interval control underground.
Why Marmato matters in Colombia
Marmato has long been one of Colombia’s best-known gold districts, but this expansion is about more than extending an existing mine. It is a test of whether the asset can be repositioned as a modern, mechanised underground bulk mining operation with a materially larger processing base. If Aris executes well, the project would strengthen Colombia’s role in Latin American gold production and provide a notable case study in brownfield underground transformation.
The next phase will be defined less by headline announcements and more by engineering delivery: development advance, fleet performance, plant commissioning, and ramp-up discipline. Those metrics will determine whether the operation reaches the stated objective of approximately 200,000 ounces per year.
Linkable Assets for Decision Makers
- Marmato Expansion Tracker: Key milestones for underground development, fleet delivery, and plant commissioning.
- Bulk vs. Narrow Vein Mining Framework: Operational trade-offs in mechanisation, dilution, and throughput.
- Gold Plant Ramp-Up Checklist: Throughput, recovery, availability, and commissioning metrics to watch.
