Sarvisto Graphite Project – open pit design for mining concession application

Client & context

You may recognise this situation:

• You are advising the owner of a high-grade graphite deposit in northern Sweden.
• Your resource geologists have delivered a PERC-compliant mineral resource and you now need to demonstrate Reasonable Prospects for Eventual Economic Extraction.
• You have to translate that work into a clear open pit design, haulage concept and grade–tonnage figures for an exploitation (mining) concession application.

At Sarvisto, the owner had confirmed a significant graphite resource north of Pajala and wanted to demonstrate how that resource could be mined by open pit using a realistic truck–shovel fleet and a processing plant located several kilometres away.

Challenge

The main challenge for you at this stage is to bridge the gap between the geological model and a mine plan that regulators can trust. In practice, that means answering questions such as:

• What is a sensible basis of design for bench geometry, pit slopes and ramp gradients, given the early geotechnical information?
• Which truck and excavator sizes fit your production target and pit geometry, and what does that mean for ramp width and safety berms?
• How will material move between the pit and the processing plant several kilometres away, and what haul cycle times should you assume?
• How many tonnes of graphite ore and waste will you mine bench by bench, above a defined cut-off grade?

You need coherent answers to these questions in order to support both the mineral resource inventory and the mining concession application.

Approach

From resource model to open pit basis of design

The starting point at Sarvisto was the 3D block model of the graphite deposit and the open pit optimisation completed as part of the scope of work by Gosselin Mining AB. Based on this, a practical basis of design was defined for the open pit:

• Bench height and face angle suitable for the planned production drilling and blasting.
• Catch bench width and overall slope angle consistent with the preliminary geotechnical information.
• Ramp gradient targeting 10% to balance safety, productivity and winter operations.
• Minimum mining width to allow safe operation of the selected excavator and truck fleet.

This basis of design allowed you to move from a theoretical pit shell to a workable open pit geometry that could be illustrated and defended in the concession documentation.

Equipment concept and haulage assumptions

To support your production strategy, a truck–shovel concept was developed around:

• A large front-end loader or shovel working on 10 m benches.
• 90 t class rigid mining trucks as the base case haulage unit.
• Typical uphill and downhill speeds on 10% ramps, allowing estimation of cycle times.
• Haul road and safety berm dimensions that fit the chosen truck width and tyre size.

Using these assumptions, you obtain realistic haul cycle times for the haul route between the pit and the processing plant, and you can show how many trucks are needed to meet a target annual graphite production.

Detailed pit and ramp design

With the basis of design and equipment defined, the Sarvisto open pit was laid out bench by bench:

• A final pit bottom was selected at the lowest elevation that still provides sufficient working room for the fleet.
• A continuous in-pit ramp was designed from the pit bottom to surface, with single-lane sections at depth and double-lane widths near the surface.
• Bench crests and toes were adjusted so that the pit follows the optimised shell while maintaining the desired slope profiles.
• Plan and section views were generated to illustrate the final pit geometry for the authorities and stakeholders.

The result is a clear visual and numerical description of how the Sarvisto graphite orebody can be mined by open pit.

Grade–tonnage reporting for the concession dossier

Finally, the open pit design was combined with the block model to calculate:

• Ore tonnages and average graphite grades above a defined cut-off.
• Waste tonnages within the final pit envelope.
• Bench-by-bench distributions of ore and waste to support scheduling at the next study level.

These outputs feed directly into the mining concession application and support the Reasonable Prospects for Eventual Economic Extraction that underpins the resource statement.

Results & value

For a project like Sarvisto, this work gives you:

• A defensible open pit design that links clearly to your geological model and open pit optimisation.
• A transparent equipment and haulage concept that regulators and stakeholders can understand.
• Grade–tonnage figures that show how much graphite and waste you expect to mine within the designed pit.
• Technical material that can be reused and refined in future pre-feasibility or feasibility studies.

In Sarvisto’s case, the open pit design and supporting documentation formed an important part of the mining concession application and helped demonstrate how the high-grade graphite resource can be mined responsibly in Pajala.