But deposits large and concentrated enough to be worth mining are indeed rare.
但是，沉积或富集到有开采价值的却实在难找。
Such concentrated deposits ought to make underwater mining highly efficient.
这样的集中式分布可以使水下开采效率大大提高。
Such concentrated deposits ought to make underwater mining highly efficient.
这样的集中式分布可以使水下开采效率大大提高。
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