After years of driving by the Argo mill in Idaho Springs, Colorado, we decided to turn off of I-70 and take the tour. Admittedly my interest in the mining history of the west had something to do with it.
This is a very unusual historical site and is worth a stop for those with an interest in history and mining. The facility consists of a red mill building built along the slope of the mountainside and, separately, access to the entrance of the Argo tunnel. Adult tickets cost $15 and in exchange for the fee, you get a movie and a talk on the history of the mill by a staffer, and a pack of sand for your gold panning lesson. The sample of sand is salted with gold flakes so that everyone has a decent chance of recovering some flakes.
What makes the Argo mill unusual? Several things. Most obviously, it is a gold mill that is quite well preserved. Most gold-rush era mill sites were in various stages of ruin in the early 2oth century. That this mill has been so well preserved alone makes it worth a visit. Add to that the machinery that is on display and you will get a fairly good idea of what it must have been like to work in such a place.
The other major reason for the unique quality of the Argo is it’s association and proximity to the Argo Tunnel. The 4.16 mile long tunnel was begun in 1893 and completed in 1910. The idea behind the tunnel was both simple and ambitious. In order to provide milling services to the mining districts to the north, a tunnel was constructed below the mines to provide both drainage and easy transportation to a mill.
Idaho Springs sits about 2000 ft below nearby Central City and is well situated for such a tunnel. The Central City gold district was a natural phenomenon at it’s peak. This section of the Colorado mineral belt was fabulously rich in gold and beginning with the 1859 discovery of gold, quickly became densely covered with mining claims from Idaho Springs northward to Central city and beyond. Hauling ore from the north to Idaho Springs was problematic owing to the topography. A major road was the Virginia Canyon road, also called the Oh-My-God road, and was unsuitable for hauling ore. Ideally, a mill should be below the entrance to the mine in order to make maximum use of gravity in the milling operations.
When completed, ore was moved through the tunnel by ore cart from mines to the north and received at the mill in the tipple house. The ore delivery was recorded and assayed for gold content. The business model of the mill was this- ore was purchased from the mines on the basis of assay and extractable gold was recovered. This model of operation was common. Mills and smelters were customers for the mine operators. Ore was produced at the mine and sold on the basis of assay.
According to the guide at the mill, amalgamation operations were halted in the 1930’s, allegedly due to health and safety concerns. The ore was comminuted with a ball mill and subjected to separation of the gold by shaker tables. Maybe the reason cited for ceasing Hg operations is accurate, but I’ll need to see independent verification of that.
Cyanadation was practiced at the mill as well. Not much was disclosed about this process. The guide disclosed that the mill tailings were contaminated with cyanide and mercury. As it happens, cinnabar occurs naturally in the Central City mining district, according to the guide, and can be found in spoils piles. Today this contributes to total package of contaminated leachates which may find their way into the watershed.
All in all, the Argo mill is worth a visit. Like all tourist attractions, however, you have to expect that there will be some dumbing down of the scientific and engineering details. Commonly, the emphasis in a visit to a tourist mine is on the craven details of gold mania and this tour is no different. However, I am a purist. My interest relates more to the natural history of the chemical elements than the details of blasting and mucking. So, if you can turn a blind eye to lackluster docent work, such tours are interesting and useful.