This isn't a "Herpaderp, moar minez pl0x" post. My reasoning behind suggesting the institution of mine hole decay is that, as of now, prospecting as a skill is nigh-worthless. Because if covers such a HUGE area, it means that it's only useful to the first person to gain access to rustroot in each region. After that, all of the mines in the region will be swiftly claimed, and prospecting no longer discovers them.
The thing is, it's not that all of the mines in the world are currently in use: it's just that they can't currently be found due to claim and abandonment. If the mine hole was allowed to decay and return the mine to it's "hidden" state, prospecting would once again become useful in allowing newer players to find "used" mines that have fallen out of service. I saw it suggested that prospecting should find active mines, but I don't like that idea because it should be up to the claimant to maintain repairs to their mine hole, and in doing so keep the hole off the radar, so to speak. The only reason someone would be able to prospect the hole using my suggestion would be if the claimant underwent a significant period of inactivity and allowed the mine to decay.