Compare open-pit mining and underground mining for diamonds, including typical cost, ore grade considerations, and risk profiles.

• A. Open-pit mining handles near-surface deposits with lower unit costs but greater surface disturbance.
• B. Underground mining targets shallower pipes with lower costs.
• C. Open-pit mining has higher ore grades than underground mining.
• D. Underground mining requires no blasting.

Answer: (D)

Understanding how open-pit and underground diamond mining compare hinges on depth of ore, cost structure, ore grade distribution, and safety risks. Open-pit mining is practical when the diamond-bearing rock sits near the surface. It allows high-volume production with relatively simple infrastructure, which drives lower unit costs per ton mined and processed. But the upside comes with significant surface disturbance, land-use impacts, and geotechnical or weather-related risks tied to large open pits.

Underground mining becomes necessary when ore is deeper or otherwise not economically accessible from the surface. Developing and operating underground workings requires substantial capital for shafts, declines, ventilation, ground control, and ore handling, so the cost per ton is typically higher. The surface footprint is much smaller, and underground methods can focus on higher-grade portions of the ore body, which can improve economics if the grade and geometry justify the expense. Blasting is a common part of underground hard-rock mining to fragment rock for extraction; claiming that blasting is not needed isn’t accurate.

So the statement that best captures the real contrast is that open-pit mining handles near-surface deposits with lower unit costs but greater surface disturbance. The other described points don’t align with how ore depth, costs, and blasting typically play out in diamond mining.