在露天开采的金矿中，通常矿石的质素为1至5 g/1000 kg (1–5 ppm)，, 地下硬岩开采（Hard rock mining）或是 地下开采（Underground mining） 的矿石的质素通常至少有3 g/1000 kg (3 ppm)。
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Senior Administrator for Cluff Gold,Clifford Patnelli, says mining for gold in the hard rock will be a first for Sierra Leone.
VOA: standard.2010.04.22
The Elimination of Double Subsidies for the Hard rock Mining Industry Act takes on depletion allowances for mineral extraction based industries.
FORBES: Connect
There is free access to 216 million acres or about 9% of all public land for the purposes of hard rock mining.
It will be challenging for the company as it transitions from soft-rock mining to hard-rock mining.
FORBES: High Costs In 2013 Will Continue To Be A Hurdle For IAMGOLD
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