Why can deeper parts of a mineral deposit require a higher ore grade to be profitable?

Deeper parts of a mineral deposit often require a higher ore grade to be profitable because the costs associated with extracting and delivering that ore to a mineral processing plant are significantly higher than those for surface-level deposits.1

As mining operations transition from open-pit methods to underground techniques at greater depths, several factors drive up these costs:

• Equipment Constraints: Underground mining equipment is generally smaller than that used in open pits due to limited access and challenging ground conditions, which reduces productivity per worker.2
• Operational Complexity: Underground mining requires specialized development, such as creating stopes, which is expensive on a per-ton basis.2
• Geologic Pressures: As depth increases, the weight of overlying rock and lateral pressure intensify, necessitating more complex rock mechanics and engineering to manage structural stability and hazards like rock bursts.2

To maintain profitability, the break-even grade—the point where costs equal revenues—must be met. Consequently, deeper ore must have a higher concentration of the valuable mineral to offset these increased operational expenses.1