My guess would be when there is not a surplus of Rupees flooding the market from Death Mountain.
But there is a few problems and things to note with that.
1) Death Mountain would have to become inactive, and the mountain range would have to be completely stripped of all rupees.
2) If that were to happen, to gorons would have to work in other lands to gain the Minerals/Rupees needed for every day life, They eat rupees after all.
3) If the Gorons are devouring all of the Local currency, It would cause a wide spread Recession and conflict with the Gorons.
4) In the end it could cause the extinction of the Gorons.
5) Because of all the above, the Gorons would not let this happen in the first place. They cultivate Death Mountain and the Mountain range it belongs to. So that the Lava is always flowing from it's sources, And for that lava to be spread around the land in rotations, so that there is always Rupee Cristal forming at all times through out the Death Mountain Range. The Gorons are Miners yes, But it may be more accurate to say they are farmers of gems, crystals, and valuable minerals.
Now that I think about it, The Labrynna Regime would benefit greatly by a trade alliance with the Gorons.

They would no longer have to strip mine or use lesser forms of mining to get the mettle and ore they need for there industry. Also they would be able to again in mass quantities the minerals needed for gunpowder.
