Mont. Code Ann. § 15-23-804

The department shall prepare from the reported valuation a tax roll that must be transmitted to the county treasurer on or before September 15 each year. The county treasurer shall proceed to give full notice to each metal producer and to collect the taxes due at the times provided for in 15-16-102, and any delinquencies in the payment of the taxes are subject to the interest and penalties provided for in 15-16-102.