When gold is mined, the materials pulled out of the mine are often dumped in piles on the ground nearby. There, the toxic minerals in them can leach into the ground, killing vegetation as well as animals and also seeping into the drinking water sources of local communities. Buying a ring of reclaimed gold means that no new gold was mined for your ring.
Consider these other alternatives to buying newly mined gold: buying a vintage ring and giving new life to a family heirloom.
Keep in mind as you shop that strict interpretation of Jewish law and most tradition-minded rabbis require the use of plain gold rings without any gems or etched designs.