A stope is an underground chamber where ore is actually extracted from the earth. While tunnels, shafts, and drifts serve as passageways to reach valuable mineral deposits, the stope is where the real mining happens. These excavated voids can be massive, sometimes stretching more than 100 meters deep, and their shape roughly resembles a rectangular prism carved out of rock.
How a Stope Works
Think of an underground mine as a network of hallways leading to rooms. The hallways are the access tunnels, and the rooms are the stopes. Miners drill into ore-bearing rock inside the stope, load it with explosives, blast it loose, then haul the broken rock (called “muck”) out through connecting tunnels to the surface. The ore eventually reaches a processing plant where valuable minerals are separated from waste.
The broken ore typically falls to the floor of the stope, where vehicles called load-haul-dump machines (LHDs) scoop it up and carry it to an ore pass, a vertical chute that drops the material down to a haulage level below. From there, trucks or rail cars transport it out of the mine. This cycle of drilling, blasting, and hauling repeats as miners work through the ore body slice by slice.
Three Categories of Stoping Methods
Underground mining methods fall into three broad classes based on how the surrounding rock is managed: unsupported, supported, and caving.
- Unsupported methods rely on the natural strength of the rock itself. The ore body and surrounding walls are stable enough that only minimal reinforcement is needed to keep the opening from collapsing.
- Supported methods require engineers to add major structural support, such as backfill material or pillars, to prevent the stope walls and ceiling from caving in.
- Caving methods take the opposite approach entirely. Instead of preventing collapse, these methods depend on the rock caving under its own weight. The ore body must be weak enough to break apart naturally once support is removed, and this controlled collapse is what delivers the ore.
The choice between these categories depends on the rock’s strength, the shape and angle of the ore body, how deep it sits, and economic factors like how much waste rock you can tolerate mixing in with the ore.
Cut and Fill Stoping
Cut and fill is one of the most common supported methods. The concept is straightforward: mine a horizontal slice of ore, then completely backfill the empty space before mining the next slice. A jumbo drill bores holes into the rock face, the holes are loaded with explosives and detonated, and an LHD scoops the broken ore and drops it down an ore pass to a lower haulage level.
Each slice is typically between 10 and 30 feet thick, depending on how stable the surrounding rock is. Once a slice is fully mined out, backfill material is pumped or placed into the void. This fill becomes the new floor, and miners stand on it to drill and blast the next slice above. The process works upward through the ore body one layer at a time.
Shrinkage Stoping
Shrinkage stoping uses the broken ore itself as temporary support. After each blast, most of the shattered rock stays inside the stope, propping up the walls while miners stand on the rubble to drill the next round of holes overhead. Only a portion of the ore is drawn off after each blast.
This partial removal is necessary because rock swells when it breaks, increasing in volume by 30% or more. Without drawing some material out, there wouldn’t be enough room for the next blast. Each round typically removes a 10-foot slice of ore from the ceiling. Once the stope is fully mined from bottom to top, the remaining broken ore is pulled out all at once. The tradeoff is that working on loose rubble makes it difficult to move heavy equipment, so this method suits narrower ore bodies where large machines aren’t practical.
Vertical Crater Retreat
Vertical crater retreat is a bulk mining method designed for steep, thick ore bodies. Miners drill large-diameter holes downward from a level above the stope, then blast the bottom of each hole to crater out successive slices of ore. The ore body is mined from the bottom up, but the drilling and blasting are done remotely, meaning no workers need to be inside the stope during production. Broken ore falls to the stope floor, where LHDs (increasingly operated by remote control) haul it away.
What Holds a Stope Together
Keeping a stope stable is one of the most critical engineering challenges in underground mining. Engineers evaluate the rock mass using rating systems that score factors like fracture density, rock strength, and water conditions. About three-quarters of stope design studies use some version of the Mathews Stability Graph, a tool that plots the size of a stope opening against the quality of the surrounding rock to predict whether the walls will hold.
The physical reinforcement inside and around stopes typically involves rock bolts, steel rods drilled into the walls and ceiling that bind fractured rock together. When the failure zone is shallow, short bolts anchored into solid rock beyond the fractures are sufficient. In areas with deeper instability, engineers install tightly spaced short bolts closer to the surface to create an artificial support arch, backed by long cable bolts that reach into stronger rock further back. In mines with high stress levels deep underground, energy-absorbing bolts that can stretch without snapping are preferred over rigid ones. Shotcrete, a layer of sprayed concrete, often covers the bolted surface for additional protection.
Backfilling Empty Stopes
Once ore is removed from a stope, the void left behind can destabilize surrounding tunnels and future stopes. Backfilling solves this by returning material to the empty space. It also provides a convenient way to dispose of mining waste underground rather than on the surface. Three types of backfill are widely used.
- Rock backfill uses waste rock produced during mining, sometimes mixed with cement. It’s 100% waste material, making it the simplest option when large quantities of rock are available.
- Hydraulic backfill mixes classified waste from the processing plant with water and pumps it into the stope as a slurry. The water drains out after placement, leaving compacted fill behind. It uses 60 to 75% waste material.
- Paste backfill combines dewatered processing waste with water and cement into a thick, toothpaste-like consistency. It contains 75 to 85% waste material and always requires a cement binder, which makes it more expensive but stronger. Paste backfill holds its shape better and produces less drainage water than hydraulic fill.
Ore Dilution: The Economic Challenge
No stope extracts ore perfectly. Waste rock from the walls and ceiling inevitably mixes in with the valuable material, a problem called ore dilution. This waste lowers the grade of ore sent to the processing plant, increasing costs per unit of recovered mineral. Engineers classify stopes into dilution zones: under 5% is excellent, 5 to 10% is acceptable, 10 to 15% is problematic, and above 15% can seriously erode profitability. The stability of stope walls directly controls dilution. Larger stopes in weaker rock tend to experience more wall failure and higher dilution rates.
Automation in Modern Stopes
Mining companies are increasingly moving human operators out of stopes entirely. Autonomous LHD vehicles can now scoop broken ore and haul it to ore passes without a driver on board. Sandvik’s AutoMine AutoLoad 2.0 system, launched in 2023, allows operators in a surface control room to program loading profiles for each drawpoint, eliminating the need for anyone underground during mucking.
Fully autonomous systems are still maturing. In underground testing at a Finnish gold mine 750 meters below the surface, a battery-electric LHD and truck completed a full material handling cycle with no human intervention, successfully loading from an 11-meter-wide muck pile using stereo camera vision to detect the ore. In earlier trials at a Swedish test mine, 61% of automated loading attempts succeeded, with most failures caused by navigation issues rather than the loading technology itself. The technology works, but reliability in the unpredictable conditions of a real stope is still catching up to the concept.