Ore Loss Mechanisms in Diamond Layout Sublevel Open Stoping for Moderately Dipping Medium-Thick Orebodies

Deep beneath the earth's surface, vast deposits of gold, iron, and other metals lie trapped in rock layers that tilt gently rather than standing straight up. These are moderately dipping orebodies, and they hold a significant portion of the world's mineral wealth. For decades, miners have struggled to extract these resources efficiently. Traditional methods often require leaving large pillars of rock behind to hold up the ceiling, which wastes valuable ore and creates safety hazards. Other approaches involve filling the mined-out spaces with waste rock, a process that is slow, expensive, and difficult to manage. A newer technique called diamond layout sublevel open stoping offers a promising alternative. It uses gravity to pull broken rock down into collection points, allowing miners to work safely from tunnels and extract more of the resource. However, even with this advanced method, a stubborn problem remains: a significant amount of ore gets left behind, stuck in the corners and along the walls of the excavation.

The core issue lies in how broken rock behaves when it flows. Unlike water, which pours smoothly, crushed rock is a chaotic mix of jagged pieces that can jam, lock together, or slide unevenly. When miners try to pull this material out, some of it refuses to move, clinging to the floor or getting trapped between the tunnels where the collection happens. This lost material represents a direct financial loss and a waste of the planet's resources. Understanding exactly why this happens, and how to stop it, is the difference between a profitable mine and a struggling one. Researchers at Northeastern University in China set out to solve this puzzle by studying the specific mechanics of how rock flows in these tilted tunnels, focusing on three main factors: the angle of the tunnel floor, the roughness of the rock surface, and the distance between the collection points.

To investigate this, the team built a scaled-down model of a mine in their laboratory. They filled a transparent box with crushed rock that matched the size and shape of the ore found in a real gold mine. By adjusting the angle of the floor, changing the texture of the surface to be either smooth or rough, and altering the distance between the collection tunnels, they could watch exactly how the rock moved. They also ran computer simulations that tracked the movement of millions of individual rock particles, allowing them to see forces and interactions that are invisible to the naked eye. The goal was to identify the specific shapes of the leftover rock and determine which settings would allow the most ore to be recovered.

The experiments revealed that the lost ore does not disappear randomly; it forms three distinct patterns. The first is a layer of rock that sticks to the floor of the tunnel, unable to slide down because of friction. The second is a triangular pile of rock that gets stuck at the very end of a collection tunnel. The third is a ridge of rock that remains in the space between two adjacent collection tunnels, simply because the mining equipment cannot reach that far. The researchers found that the angle of the tunnel floor plays a critical role. If the angle is too shallow, the rock gets stuck in a large, uneven pile along the floor. If the angle is too steep, the total amount of rock that can be pulled out decreases because the geometry of the tunnel changes. There is a sweet spot where the flow is optimized.

The team discovered that the roughness of the floor surface is just as important as the angle. When the floor was made of rough, jagged rock fragments, the material moved much more slowly and left behind significantly more residue. When the floor was smoothed out, the rock flowed more freely, and less was left behind. This suggests that in a real mine, smoothing the floor or using water to reduce friction could improve recovery. The distance between the collection tunnels also mattered. When the tunnels were placed closer together, less rock was left trapped in the ridges between them. However, placing them too close together increases the cost of building the tunnels, so a balance must be struck.

Through their physical models and computer simulations, the researchers pinpointed the optimal conditions for extracting this type of ore. They found that a tunnel floor angle of 40 degrees provided the highest recovery rate, capturing about 83.6 percent of the available ore when the floor was rough. If the floor was smoother, the recovery rate could reach nearly 89 percent. At a steeper angle of 50 degrees, the rock that usually sticks to the floor disappears entirely, but the overall amount of ore recovered drops slightly because the shape of the tunnel changes. The simulations confirmed that the rock tends to flow preferentially along the upper walls of the tunnel, while the particles near the floor remain compressed and stuck. This behavior explains why the floor angle and surface texture are so decisive.

The findings were not just theoretical. The researchers took their insights to an active gold mine in China and tested them in the field. They used 3D scanning technology to map the empty spaces left after mining, comparing the real-world results with their laboratory predictions. The scans confirmed that the three types of leftover rock they identified in the lab were indeed present in the mine. The theoretical loss rate calculated from their models was about 34 percent, while the actual measured loss in the field was slightly higher at 38.2 percent. The difference is likely due to the unpredictable nature of real-world blasting and the complex behavior of rock that cannot be perfectly replicated in a model. Nevertheless, the close match between the model and reality validates the approach.

The study concludes that there is no single setting that solves the problem of lost ore. Instead, it requires a careful balance of the tunnel angle, the smoothness of the floor, and the spacing of the collection points. By aiming for a 40 to 45-degree angle and managing the surface friction, mining operations can significantly reduce the amount of valuable metal left behind. This work provides a clear, data-driven guide for engineers to optimize their mining plans, ensuring that more of the earth's resources are recovered safely and efficiently. The research demonstrates that even in the chaotic world of broken rock, predictable patterns exist, and understanding them can lead to better outcomes for the industry.