One Site, Three Mills
Before we get into more archaeology, I think its important to explain some of the history of the stamp mills at Cliff. There were three, all existing in close proximity to each other but at different times and with different equipment. This post has a lot of text, and a lot of pictures to go along with it.
When the Cliff began operations in the mid-1840’s, the miners weren’t exactly sure what to make of the ore body they worked. The Cornish and German miner’s backgrounds were in mining compound ores, metals that existed in combination with other minerals, not with pure “native” metals like the copper found in the Upper Peninsula.
In Old World mining locations like Cornwall and Germany, ore had to be freed from the surrounding rock, then smelted in order to extract/coalesce the desired metal. Basically, a lot of material had to be removed from underground and then processed in order to gain a desired product. The huge quantities of mass copper found at Cliff and other early mines in these early years allowed the bypassing of these drawn out processes in favor of just chiseling and collecting the masses uncovered. The finely disseminated copper located within the surrounding trap rock could be ignored. For a mine like the Cliff, where mass copper was prevalent, dressing, stamping, and washing this “copper rock” was not a primary necessity. Producing “stamp work” was only a secondary activity.
In time, the Pittsburgh and Boston Mining Company realized that leaving the disseminated copper ore found in the rock surrounding the mass copper shouldn’t be ignored, since an ever-growing (and deepening) mine would become harder and harder to maintain at a profit. The copper rock could add to their production, and only required a small mill operating seasonally.
The first mill of the Cliff mine is not well documented in the historic record. What we know is that is existed from 1847-1850 and was situated very close to where the later, larger mill ruins sit presently. This first mill was likely of timber construction, and housed anywhere from 6-10 Cornish style gravity stamp heads powered via a small steam engine that only worked to lift the stamp heads, not drive them down. The methods used for separating the copper mineral from the sand and water after stamping were long troughs raked by men to bring the mineral to the head of the trough and let the water and sand pass down to the tail end (creating mine “tailings).
By 1849, the Cliff was realizing a profit, and plans were made to invest in and expand the mine workings, both above and below ground. A new shaft was planned at the top of the bluff (the No. 3), a stone constructed engine house was built to house a large Nicholas Vivian* built steam engine to run the hoisting from No.’s 1 and 2 shafts, and a new mill was built to replace the small, timber mill used for only a handful of years.
This new mill is what we are currently excavating. Located just behind the old mill, it was completed in 1851 and was designed to house 12 Cornish style drop stamps. Its engine (another Nicholas Vivian design) powered both the raising (but not the dropping) of the stamps as well as pumping water from underground-probably to provide water for the washing process. Soon after its completion, a fire destroyed the original mill but left the new mill undamaged.
The new mill underwent many changes over the next 20 years, as the mill crew of the mine transitioned from old technologies to newer, more efficient ones being developed in the Keweenaw during the mid-nineteenth century. The mill originally used tiered buddles (mineral again being left behind on each tier as water passed over it) and hand-operated jigs that plunged material over a screen into water and out again.
In 1856, the mill was expanded to contain 36 Cornish stamps, tripling production capacity. A 100 x 50 foot wash house was also built to extend out from the stamp room. Inside, jigs, washing tables, and circular buddles (a round vat that is swept in a circular motion to let heavier copper mineral settle at the bottom while skimming off the lighter tailings) were handling up to 100 tons of stamped rock a day. By the mid-1860’s, automated jigs (not requiring a man to “plunge” the screen and material) were installed, and the circular buddles were bypassed in favor of a 120 ft. long, 4 tiered launder that was shaken via rods connected to the same 1851 steam engine. In order to contain this 120 ft launder, another 50 feet were added to the wash house. 1867 saw the installation of new slime washing machines. Slimes were the finest of the tailings, but still often contained large percentages of copper mineral. The stamps were overhauled and their wrought iron stems and cam shaft replaced by Bessemer steel ones.
All of these changes were brought on by a combination of events: an ever-increasing dependence on stamp work as the mass copper became less and less prevalent the deeper the mine went, and a rise in copper prices due to the Civil War. By the end of the 1860’s however, no amount of technological adaptation and efficiency could make up for a dwindling ore body, and the Pittsburgh and Boston Mining Company pulled up stakes and sold the Cliff in 1871 for $100,000.
Much of the mine’s equipment was sold to new mines or to these new investors. The mill kept up production at a smaller scale for the next decade, but by the late 1880’s (at the least), the mill was abandoned and soon collapsed. A new mill, called “Warren’s Mill,” was built around 1910 by a man named Henry Warren, who hoped to re-outfit the Cliff after it was worked unsuccessfully by the tamarack Mining Company. This mill housed only 8 drop stamps, and was built on the ruins of the previous mill. It took advantage of the earlier mill’s boiler room and smoke stack, but was powered by a steam engine we (at this time) know nothing about. For washing copper, a slanted table with a riffled surface was used (a Wilfley Table).
The construction of this mill is both a blessing and a curse to our current work. Its construction buried many in-tact remains of the earlier 1850’s-1860’s operations in some places, while obliterating these in others. This mill was very well documented by photography, and if you search for “Cliff” and “Stamp Mill” in the Keweenaw Digital Archives, you will see both this mill inside and out. This images provide some great details about the stamps themselves, though at this time I am not sure if the stamps used in Warren’s mill were original Cliff stamps or brought in from elsewhere. This mill burned sometime in 1926-27, and its equipment was likely scrapped not long after.
So there you have it. One site, three mills.
*I’ll get around to explaining Nicholas Vivian’s significance in another post.