以大理岩为原岩的矿石品质优良，以斜长角闪岩为原岩的矿石品级较低。
Grade of ore formed from marble is higher, that formed from amphibolite is lower.
如今新开发的铜矿还不多，而随着旧铜矿开采的深入，上等品级的矿石已逐渐开采完，矿石品级已不如从前。
As older mines get deeper and the choicest parts of deposits become exhausted, ore grades have declined.
由于目前商品级的矿石可能用完，富集过程是重要的。
A concentration process is important now that the depletion of high grade ores is possible.
由于目前商品级的矿石可能用完，富集过程是重要的。
A concentration process is important now that the depletion of high grade ores is possible.
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