Not Your Grandfather’s Mining Operation

It’s a new millennium.
Like other global industries, mining has undergone dramatic changes in recent years, bringing it firmly into the world of 21st century high technology. The mining industry has availed itself of the high-tech tools necessary to compete in today’s global economy. It is also a better steward of the environment, using modern mining practices and technology to do everything reasonably possible to minimize disturbance and reclaim the land following operations. To further ensure accountability and responsibility, the industry is closely monitored through state and federal laws and regulations.

Today, people accept the fact that the government sets pollution standards for a variety of industries, including mining. Old mining sites are being reclaimed, replanted and restored. Both state and federal regulatory agencies keep a sharp eye on industry practices. And, in some instances, the mining industry and environmental groups are working together to minimize the effects of mining on land and waterways.

Large resources, modern operations without smelters
The state of Minnesota estimates that the more than 4 billion tons of crude, non-ferrous ore here are perhaps the largest deposits of these base and precious metals in the United States. The category of “strategic” metals – which include platinum, palladium and nickel – as well as gold, silver and copper deposits were discovered and initially explored in the 1950s and 1960s. However, due largely to lack of a viable processing technology to economically and effectively treat these ores, the saleable products could not be produced.

The last 15 years have brought about remarkable changes in the industry. Hydrometallurgical processes, which subject the concentrates produced from the crude ore to a medium-high temperature and pressure in a sealed steel vessel – an autoclave – make it possible to selectively extract the valuable components and treat and contain all air or water emissions as required for environmental compliance.

Why is non-ferrous mining an issue?
The mining of sulfide deposits containing copper and nickel has historically been at the heart of most of the environmental concern. In mining’s earlier years, environmental impacts were not well understood and not a matter of significant concern either. However, this legacy of environmental damage is not indicative of new mines and mining practices.

If naturally occurring buffering minerals and rocks such as limestone are not present in sufficient quantity, sulfide minerals can generate acidity when exposed to oxygen and water. This acidity is commonly referred to as Acid Rock Drainage (ARD), which can form when sulfide-bearing rock is exposed to oxygen in the air and water from precipitation. Water that makes its way through an unprotected stockpile of sulfide minerals that has been left exposed to the atmosphere can contain dissolved metals and low pH values. The sulfide, however, contains the desired metals and is sent to the plant for processing.

If ARD is left uncontrolled, it can reach streams or groundwater.