What’s an epithermal deposit?
Unlike porphyries, epithermal deposits are not large. They are often rather small, yet appealing to mining companies because of their high grades and shallow depths.
The minerals in an epithermal deposit are often concentrated in veins, which are often close to the surface. On average, the mineralized veins in an epithermal deposit are found at 600 meters deep. The shallowness of these deposits, combined with the high grades makes them easy to mine, in an economic sense.
Epithermal deposits are often found on islands, or around hot springs. There are some forming in the US right now. Think about the Yellowstone hot springs.
Epithermal deposits are lode deposits, like VMS, and Carlin-type deposits, all of which are highly sought-after by gold exploration companies because of their higher concentration of gold, which oftentimes means higher grades.
Gold is the main metal found in epithermal deposits.
A very good in-depth explanation on epithermal deposits, for non-technical people, can be found in the following video:
Further literature can be found here.