All surface oil and gas well equipment and submersible pumps and sucker rods located on oil and gas leaseholds or lands shall be separately valued for assessment as personal property, and such valuation may be at an amount determined by the assessors of the several counties of the state, approved by the administrator, and uniformly applied to all such equipment wherever situated in the state. All other subsurface oil and gas well equipment, including casing and tubing, shall be valued as part of the leasehold or land under section 39-7-102.