All mines and mining claims, both placer and rock in place, containing or bearing gold, silver, copper, lead, coal or other valuable mineral or metal deposits, after purchase thereof from the United States, shall be taxed at the price paid the United States therefor, unless the surface ground, or some part thereof, of said mine or mining claim is used for other than mining purposes, and has a separate and independent value for such other purposes, in which case said surface ground or any part thereof so used for other than mining purposes, shall be taxed at its value for such other purposes, and all machinery used in mining, and all property and surface improvements upon mines or mining claims, which have a value separate and independent of such mines or mining claims and the net annual proceeds of all mines and mining claims shall be taxed: provided, that nothing in this chapter contained must be construed so as to exempt from taxation improvements, buildings, erections, structures or machinery placed upon any mining claims, or used in connection therewith: provided that all mineral rights reserved to any grantor, except the United States or the state of Idaho, by the terms of any conveyance of lands other than lands acquired under the mining laws of the United States shall be assessed for taxation purposes at the rate of not less than five dollars ($5.00) per acre of the mineral rights so reserved, to be assessed against the recorded owner thereof. When, in the opinion of the county assessor, the value of reserved mineral rights does not warrant the expenditure to appraise and assess such value, such de minimis values need not be appraised or assessed, but the failure to assess such values does not constitute a failure to pay such taxes on the part of the owner, and does not constitute a delinquency on the part of the owner.