Mont. Code Ann. § 39-3-501

For the purposes of this part, all the provisions of part 2 of this chapter extend to and govern every person, firm, partnership, or corporation engaged in the business of extracting or of extracting and refining or reducing metals and minerals or mining for coal or drilling for oil, except persons, firms, partnerships, or corporations that have a free and unencumbered title to not less than one-half the fee of the property being worked. For this purpose, an outstanding unpaid or unredeemed tax lien certificate is not considered an encumbrance.