Montana Earth Science Picture of the Week

From 1884 until the early 1900s much of the ore mined in Butte was brought to a smelter (above left) near Anaconda. The smelter was located where the Old Works Golf Course sits today (above right). In both photos the city of Anaconda can be seen in the background. At the smelter copper was removed from the ore using various processes, including melting (smelting means separation by melting). The smelter generated tremendous amounts of tailings and slag, which were piled onto the land in the surrounding area. In the early 1900s a newer smelter was built on the opposite side of the valley and the older one, dubbed "the Old Works" (above left), was dismantled and abandoned.

Like many of the mine wastes in the Butte-Anaconda area, tailings around the old smelter contain an abundance of sulfide minerals. This causes a problem known as "acid mine drainage". As air and water interact with the sulfur in these minerals, the water becomes acidic enough to dissolve metals from rock material that it comes into contact with. The EPA recognized that the acid drainage situation at the Old Works smelter posed a threat to the quality of surface and groundwater in the Anaconda area, so in 1983 the EPA designated it as a superfund site, requiring that the mess be cleaned up.

In 1989, a group of people organized an effort to promote the construction of a "world class" golf course on the old smelter site. Through the cooperation of community, ARCO, State and Federal Agencies along with golf legend Jack Nicklaus, ground was broken on May 26, 1994. Since the course doubles as a superfund cleanup site, there were many design considerations not found in most golf courses.

For one, the design included the construction of a "cap" to prevent water from soaking through the tailings that underlie the fairways, roughs, and native areas. The cap consists of two or three layers depending on the concentration of tailings in the subsoils. The top layer consists of six inches of topsoil, which serves as a growth medium for the grass. Beneath that is a layer of clayey soil 12 to 15 inches thick. Clay is fairly impermeable, so this layer helps keep water from soaking down any farther. Just beneath the clay is a two-inch layer of crushed limestone spread over the site. Since limestone is mostly calcium carbonate, it will counteract the potential acidifying effects of the tailings. Calcium carbonate is the active ingredient in products such as TUMS and ROLAIDS. So, if any water soaks though the layer of clay, it will become slightly "basic" when it encounters the crushed limestone. Then as that water soaks down into the tailings, it will neutralize the effect of acid mine drainage caused by sulfide minerals in the tailings. Hence, the "cap" keeps the water from becoming acidic and then contaminating groundwater beneath the course.

tailings: rock material that remains after the processing of crushed ore in order to make a concentrate of the desired metal(s)

slag: Ore is melted during the process called "smelting". The desired metals sink to the bottom of the molten material and are removed (by draining). The other rock material is allowed to cool and solidify. This solid waste material is the "slag".

Term: impermeable