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Neither open-pit nor underground mining is automatically the better choice for a gold deposit. A useful comparison tests each project plan against the same resource model, study date, production schedule, cost assumptions and site constraints; the deposit’s geometry and the work required to reach its ore shape the result.
What differs between open-pit and underground plans?
An open-pit plan removes overburden and waste rock to expose ore, then mines it in benches. Its economics depend on more than the cost of moving a tonne of rock: the plan must account for how much waste has to be removed, pit geometry, slopes and haul distances as well as the ore recovered.
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An underground plan first develops access to the orebody, using shafts, declines or drifts, then advances workings and extracts ore. Development, ground support, ventilation, dewatering, haulage and, where planned, backfill all affect the schedule and cost. Ore may be hoisted from deep workings or moved by train or conveyor in shallower mines, as described in a historical U.S. EPA technical profile.
Surface mining is often considered for large, shallower deposits with limited overburden; underground methods may suit deeper or higher-grade zones. These are tendencies, not thresholds or a method-selection rule. Deposit shape, continuity, grade distribution, mineralogy, data confidence and engineering constraints can change the answer. The U.S. EPA’s profile and a Virginia Department of Energy report both describe these considerations; the Virginia guidance is geographically specific, not a substitute for the rules and conditions at another site.
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Compare the plans on the same basis
Use the project’s technical reports and supporting studies to answer the same questions for each option. The comparison is only meaningful if the plans use aligned assumptions and disclose where they differ.
| Comparison area | Open-pit plan | Underground plan | What to align |
|---|---|---|---|
| Ore available to mine | Ore inside the pit design, given the assumed pit shell, slope geometry and stripping ratio. | Ore accessible after accounting for development, mineable shapes, dilution and recovery assumptions. | Use the same resource model, resource classification and cutoff criteria, and identify any changes between plan cases. |
| Access and timing | Pre-stripping, benches and haul roads determine when ore can be delivered. | Shafts, declines or drifts, development and stoping sequence determine when first ore and planned throughput are possible. | Compare first production, ramp-up and steady-state dates, not just the stated mine life. |
| Material movement and equipment | Total tonnes moved, fleet requirements, haul distances and pit sequence drive the schedule. | Development metres, stoping sequence, haulage, ventilation and ground-support requirements drive the schedule. | Compare total material movement and the equipment and infrastructure needed, rather than ore tonnes alone. |
| Processing | Check ore types, crushing, leach or mill route, recoveries and tailings assumptions. | Check whether underground ore uses the same flowsheet or requires a distinct processing route. | Mining method does not by itself determine processing; compare ore characteristics and recovery assumptions. |
| Economics | Include waste stripping, haulage, pit infrastructure, processing, sustaining capital and closure. | Include development, ground support, ventilation, dewatering, backfill where applicable, haulage, processing, sustaining capital and closure. | Align currency, price deck, estimate date, study level, tax, discount rate, cost scope and production schedule. |
| Site constraints and impacts | Review slope stability, land disturbance, water management, waste placement and nearby receptors. | Review ground conditions, ventilation, water inflow, subsidence potential, access and emergency systems. | Use the relevant project’s studies, permits and mitigation plans; do not infer a universal impact or safety ranking from the method. |
How to review two project plans
- Confirm what each plan actually evaluates. Record the report date, study level, resource basis and whether the case is a proposed operation, an operating mine’s life-of-mine plan or an assessment of alternative methods. A preliminary economic assessment (PEA), feasibility study and operating-mine technical report do not have equivalent scope or certainty.
- Check that the geology is comparable. Establish whether both plans use the same resource model and classifications. Note differences in cutoffs, deposit zones, grade distributions, mineralogy, dilution and recovery assumptions. If plans mine different parts of a deposit, describe that distinction rather than treating the methods as interchangeable alternatives.
- Trace the sequence from access to saleable product. Follow the schedule from pit pre-stripping or underground access development through ore delivery, ramp-up, processing and steady-state output. Identify what must be built or advanced before planned production is achievable.
- Reconcile the full cost and revenue assumptions. Put estimates on a common currency and date basis, and check metal-price assumptions, throughput, recoveries, tax treatment, discounting, capital and sustaining costs, closure provisions and included cost categories. If a report does not state a comparable value, leave it unresolved rather than filling the gap with another mine’s figure.
- Read the site studies alongside the mine schedule. Review geotechnical and hydrological work, impact assessments, permits, mitigation, property access, infrastructure and community constraints. A technically attractive mine shape is not a complete project plan if its enabling conditions or impacts are unaddressed.
Why headline cost and grade figures can mislead
A unit cost per tonne moved, a mining cost per ore tonne or a reported grade is meaningful only in the context of the material included, the schedule, the mine life and the study assumptions. In an open pit, low unit costs for moving rock do not show how much waste must be moved to expose the ore. Underground costs likewise depend on access development and the mine-specific systems needed to extract and transport ore.
Nor is a resource grade an apples-to-apples method score. A combined-method project can assign different cutoffs and mine different zones to each method. For example, Centerra Gold / AuRico Metals’ Kemess technical report, effective 31 December 2025, reports 130 million tonnes of indicated open-pit resources at 0.32 grams of gold per tonne and 22 million tonnes of indicated underground resources at 0.93 grams per tonne. These are resource estimates from a PEA, not mineral reserves. The report uses different cutoff bases for the two methods and schedules open-pit mining to begin three years before underground production; it declares no mineral reserves from the PEA.
Reported costs also cannot be generalized from one mine to another. AngloGold Ashanti’s 2026 Geita technical report summary, current at 31 December 2025, estimates $683 million in total open-pit mining costs and $723 million in total underground mining costs over the reported life-of-mine plan. Those are project-level estimates tied to that plan’s scope, geology and assumptions, not evidence that open-pit mining is universally cheaper.
What project examples can—and cannot—show
Mine-method selection follows the deposit
The CK Gold technical report says its open-pit method was selected based on the deposit’s near-surface location, disseminated mineralization and pit-optimization results. It also describes sector-specific slope criteria and recommends continued monitoring. That illustrates why geotechnical design belongs in a project comparison; its slope criteria should not be transferred to another site.
Study assumptions belong beside the headline result
Orla Mining’s 2026 South Railroad feasibility report describes a proposed open-pit operation with a planned ten-year mine life and a 4.00:1 strip ratio. Those are estimates for that project. Their value to a comparison is that they show why a mine-life figure or production plan should be read with the underlying schedule and operating assumptions, not as a generic characteristic of open-pit mines.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What a sound comparison can conclude
A defensible conclusion identifies which plan is supported by the deposit model, engineering design, schedule, economics and site-specific approvals—and which assumptions drive that result. If the plans use different study dates, resource bases or cost scopes, state that they are not directly comparable and specify what would need to be reconciled. The comparison axes are a framework for reviewing project documents, not a substitute for qualified engineering review.
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