Anatomy of a Mill (Rock Bins)
The first stop for any rock entering a Copper Country stamp mill is one of several large storage bins that sit up and behind the mill’s stamp batteries. Since the rock will be transported through the mill primarily by gravity, these bins sit at the highest point of the mill complex. The bins are filled from overhead via an elevated trestle, from which rock cars empty their loads between the rails and down into them. In the photo above, you can see both the elevated trestle and the rock bins sitting below it.
These bins were used to provide a constant supply of rock to a mill’s stamps, a requirement of over 500 tons a day for each of a mill’s stamps. Rock would be fed into the stamp’s mortar box (where the actually crushing of rock is carried out) by means of a long metal chute. A constant stream of water was sprayed over the chute to help wash the smaller pieces of rock down into the mortar. Here’s a look at what a typical rock bin might of looked like (poor artists rendition mind you):
Like throughout the mill complex it is gravity that does most of the heavy lifting here, the flow of rock down the chute stopped by small door. The door is controlled by a worker who uses it to control the flow of rock down the chute and into the stamp’s mortar. In order to automatically signal the need for more rock, the stamp was outfitted with a mechanical device similar to the “squeaker” on a car’s brake pads. When the rock level in the mortal was too low, a “bonnet” attached to the stamp would drop low enough to strike a iron rod and make a ring.
This image is from “The Copper Mines of Lake Superior” by T.A. Rickard, via Google Books online archives. It is taken on a mill’s “feeding floor” where the rock is dumped from the bins into the mortar box. On the left you can see the chute itself, which feed into the stamp itself which is on the right. This is just the upper portion of the two-story stamp - the lower portion (including the mortar box and stamp itself) sits below here.
At the Mohawk Mill, where we are currently exploring, there is unfortunatley very little left of the rock bins themselves. This is often the case, as these bins were made of steel and were scrapped quickly after a mill’s abandonment. What should remain, however, is the large concrete foundations on which these massive bins sat. Interestingly there’s no evidence of these at the Mohawk Mill either, which is rather odd. However we were able to discover some remains at the Champion Mill, which we featured on one of our first explorations here at CCE. The photo above is a close look at those remains - the large concrete foundation on which the rock bins once sat. The stamps would of sat just to the left in the photo, up along the wall.
Moving back a bit, we can take in a larger view of the wall and fit it in with its surroundings. Over the top of the wall would sat a series of steel bins, followed by an elevated trestle running right over top of those bins. Here at Freda you can see the old concrete pillars which once supported that trestle. Below the trestle and the bins were the stamps, siting in a line up along the rock wall.
Now about those stamps….