Why are only a small percentage of known diamond deposits mined?

The small percentage of known diamond deposits that are mined is primarily due to profitability concerns. Not all diamond deposits are economically viable to extract. Factors influencing profitability include the cost of extraction, processing expenses, and market prices for diamonds. If the cost of mining a deposit exceeds the potential revenue from selling the diamonds, it is deemed unprofitable and remains unexploited.

In contrast, factors like rarity, accessibility, and the difficulty of locating deposits play a role in the overall landscape of diamond mining but do not directly reflect the primary reason for the restraint in mining known deposits. While some deposits may indeed be rare or hard to locate, their actual profitability is what ultimately governs whether they are actively mined or left untouched.