1: Gold, silver, lead, copper, iron, oil, steamcoal, Feerozah, Aqeeq, alum, salt or any other mineral are from Anfaal, which means that they belong to Imam (A.S.). But if anyone extracts them without any religious impediments, he can own them. And when they are of prescribed quantity, Khums must be paid on them.
2: The taxable limit of a mineral is 15 common mithqals of coined gold i.e. if the value of a thing which is extracted from a mine reaches 15 mithqals of coined gold, the person concerned should pay Khums on it, after deducting from it the expenses which he has incurred.
3: Chalk, lime, fuller's-earth and red clay are, as an obligatory precaution, minerals, and one who extracts them, is required to pay Khums if the value of that mineral reached the prescribed taxable limit. This will become obligatory without deducting annual expenses.
4: If a person acquires something from a mine, he should pay Khums on it whether the mine is over the ground, or under, and whether it is located in an owned land, or at a place which has no owner.
5: If a few persons jointly extract something, and if its total value reaches 15 mithqals of coined gold, if the value of the share of each one is less then 15 Mithqals then Khums in not wajib.
6: If a person extracts mineral by digging a land belonging to another person without his consent, the Fuqaha have said that it belongs to the owner of the land. But this is a matter of Ishkal, and a better alternative is that they come to some understanding between them, and if that fails, reference should be made to the Mujtahid for his decision.
These laws are according to Aayatullah Sistani's Fataawa.