Mont. Code § 82-2-402
A person, association, or corporation that buys ore upon an agreement to pay for it in an amount dependent upon the metallic contents or that smelts any ore shall retain from the pulp or crushed ore, as the ore is sampled, a quantity of not less than 50 pounds out of each ton of ore. The quantity must be selected regularly and at equal intervals from any lot of ore bought or to be smelted, and the person, association, or corporation shall keep this quantity separate from any other ore or pulp for a period of 30 days or until full settlement is made and accepted by the shipper. Until full settlement is made and accepted, the ore shipper or the shipper's agents or representatives may take any part from the quantity retained for the purpose of sampling or assaying that part. However, the value of any part taken by the owner or shipper may be deducted from the total value of the ore delivered by the owner or shipper.
§ 82-2-402, MCA