There commonly exist pyrite minerals in coal-bearing strata in one region, but it is difficult to separate.

某地区煤系地层中普遍产出硫铁矿，但非常难选。

youdao

There commonly exist pyrite minerals in coal-bearing strata in one region, but it is difficult to separate.

某地区煤系地层中普遍产出硫铁矿，但非常难选。

youdao