There are numerous recent headlines of Gem Mines or Gem Collectors being included in the next Clash of Clans update. These headlines are being reported on various Clash of Clans or mobile games related websites.
However, when reading the original source of the report, this is merely a suggestion by the writer and not a quote from Supercell or an insider.
The only comment from Supercell is that they have ruled out the introduction of Gem Mines. This is probably because they already have something similar, these are random obstacles and gem boxes which appear in your village and produce gems.
Gem Mines should be filed under “Ruled Out”.