15-23-503. Net proceeds -- how computed. (1) The department of revenue shall calculate from the returns the gross product yielded from a mine and its gross value for the year covered by the statement and shall calculate and compute the net proceeds of the mine yielded to the person engaged in mining. Except as provided in 15-23-515 through 15-23-518, net proceeds must be determined by subtracting from the value of the gross product of the mine the following:

(a) all royalty paid or apportioned in cash or in kind by the person engaged in mining;

(b) all money expended for necessary labor, machinery, and supplies needed and used in the mining operations and developments;

(c) all money expended for improvements, repairs, and betterments necessary in and about the working of the mine, except as provided in this section;

(d) all money expended for costs of repairs and replacements of the milling and reduction works used in connection with the mine;

(e) depreciation in the sum of 6% of the assessed valuation of the milling and reduction works for the calendar year for which the return is made;

(f) all money actually expended for transporting the ores and mineral products or deposits from the mines to the mill or reduction works or to the place of sale and for extracting the metals and minerals and for marketing the product and the conversion of the product into money;

(g) all money expended for insurance and welfare and retirement costs reported in the statement required in 15-23-502;

(h) all money expended for necessary labor, equipment, and supplies for testing minerals extracted to satisfy federal or state health and safety laws or regulations, for plant security in Montana, for assaying and sampling the extracted minerals, for the cost of reclamation at the site of the mine, and for engineering and geological services conducted in Montana for existing mining operations but not including services beyond the stage of reduction and beneficiation of the minerals.

(2) In computing the deductions allowable for repairs, improvements, and betterments to the mine, the department shall allow 10% of the cost each year for a period of 10 years.

(3) Money invested in mines or improvements may not be allowed as a deduction unless all machinery, equipment, and buildings represented by the money are returned to the county in which the mine is located for assessment purposes at the level of assessment of all other property in the county.

(4) Money invested in the mines and improvements during any year except the year for which the statement is made and except as provided in this section may not be included in the expenditures, and the expenditures may not include the salary or any portion of the salary of any person or officer not actually engaged in the working of the mine or superintending the management of the mine.