Idaho Mining Technology

Modern prospecting begins with a field study conducted by the Idaho Geological Survey. Thousands of core samples are drilled and tested and engineers develop a computer model of the site. The average cost of one of these studies is $250,000.00.
Before a single shovel of dirt is moved, environmental and engineering studies are conducted. An Environmental Impact Statement, state and federal permits and a period for public comment are also required.
In a surface mining operation, topsoil and non-mineral rock is removed and stockpiled for future reclamation. Benches or steps are cut on the sides of the pit to stabilize surrounding rock and minimize erosion.
In underground mines, vertical shafts and horizontal tunnels are bored to reach the mineral vein. Some silver mines in Idaho are over a mile deep.

Processing the Ore

Once the rock is blasted, shovel operators load ore onto trucks bound for the concentrating mill. Here, ore is crushed into fine particles, mixed with water and chemicals and sent through a series of flotation circuits. Air pumped into the solution causes the ore particles to float to the top where they are skimmed off.

Leaching

Low-grade gold and silver are concentrated by a process called leaching. This is where ores are treated with a chemical solution designed to dissolve the precious metals.
In a heap leach operation, ore is first crushed and stacked on a clay pad covered with a leak-proof liner. The chemical solution slowly seeps through the ore. The solution, now rich in dissolved gold and silver, is collected and processed.

Vat leaching moves ore through a series of vats, where gold and silver are dissolved by a chemical solution. The metals are recovered from the solution and the resulting “filer cake” is melted to produce a gold/silver mixture called “dore” (pronounced “door-ray”). These 50-pound dore buttons are shipped to a refinery where pure gold and silver are produced.

Reclamation

All land disturbed by mining exploration activities is reclaimed whether or not minerals are found.  This can cost thousand of dollars and the reclamation is guaranteed through bonds the exploration company posts with federal and state agencies. 

When minerals are found and a surface mine is developed, all land disturbed by that mining is reclaimed.  Sometime areas that have been mined are reclaimed at the same time that minerals are being extracted from other areas of the mine.  The reclamation of these mines is guaranteed through bonds the mining operator posts with federal and state agencies.  The total cost of reclamation for major surface mines are usually millions of dollars.