The 1.4 billion year old deposit formed on the seafloor around a “black smoker” type hot springs system. In this type of sea bottom hot spring, hot water with high concentrations of dissolved metals and sulfur vent onto the seafloor, and encounter very cold seawater. The change in temperature and chemistry cause the metallic elements including copper to bond with other elements and precipitate onto the seafloor as metal-bearing minerals. These build up in sheet like layers that can be mined.
Category About the Johnny Lee Deposit
Besides copper, the Johnny Lee deposit hosts important quantities of both cobalt and silver. Further metallurgical testing will determine whether we can recover these economically. There is a small amount of gold in the Johnny Lee lower zone, but not enough to be economically viable.
Although there are active fault zones in Montana, the fault closest to the deposit called the Volcano Valley Fault is dormant. This is a major fault zone passing between the upper and lower zones of the Johnny Lee deposit. Current geologic interpretations indicate that this fault is long dormant (80 million years) and poses no threat to the mining operation or environment.
The Johnny Lee deposit at Black Butte is named for a homesteader/prospector who lived above the deposit in the early 1900s. The mineral deposit includes two sheet-like zones rich in extremely high grade copper-iron-sulfide (chalcopyrite). It is the second highest grade copper deposit currently under permit in the world. In fact, it is more than 10 times higher than in most modern surface mines.