Taxation of mines

All mines and mining claims, both placer and rock in place, containing or bearing gold, silver, copper, lead, coal or other valuable mineral 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 such mine or 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, as provided by law; and all the machinery used in mining, and all property and surface improvements upon or appurtenant to mines and 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 as provided by law