43 CFR §3832.44

1. (a)If you located your tunnel site in good faith, you may acquire the right to any blind veins, ledges, or lodes cut, discovered, or intersected by your tunnel, by locating a lode claim, if they—
   1. (1)Are located within a radius of 1,500 feet from the tunnel axis; and
   2. (2)Were not previously known to exist on the surface and within the limits of your tunnel.
2. (b)Your site is protected from other parties making locations of lodes within the sidelines of the tunnel and within the 3,000-foot length of the tunnel, unless such lodes appear upon the surface or were previously known to exist.
3. (c)You must diligently work on the tunnel site. If you cease working on it for more than 6 consecutive months, you will lose your right to possess all unknown, undiscovered veins, lodes, or ledges that your tunnel may intersect.