When I set out to build an HO model of a 19th-century stamp mill, I wanted a particular kind of mill— a pan mill. Amalgamation pans were developed during the California gold rush and used to coax gold and silver from stubborn ores from the 1860s through the end of the century. They were common in places like Nevada's Comstock region until better technology— vanners, shaking tables, cyanide, and flotation— replaced them.
I was interested in the mines of Bodie and Eastern California, where pan mills were used extensively. The model is not an exact replica, but it's named after a mining operation that used to be a family property (now it's a historical monument) outside of Mammoth Lakes, California.
Stamp mill models need easily-viewed interior detailing, so I designed mine to dismantle effortlessly. The one-piece walls and roofs are attached with strategically-located brass wire pins. Roofs and right side come apart in less than a minute.
The interior floors and framing are built of basswood. The walls and roofs are hot-press illustration board, with each piece of wood scribed and individually painted. Batts were made with chart tape. Grandt Line provided window and door castings. Campbell shingles completed the roofs.
The base is insulation foam textured with wallboard paste and real dirt. The model was meant to be part of a larger scene with the mines and tunnels "uphill" behind the structure.
The original 40-stamp Mammoth Pan Mill was built in 1878-79 outside of Mammoth Lakes, California. It was only used during Mammoth's brief gold mining boom and abandoned in the early 1880s. It lay derelict until it was burnt by the U.S. Forest Service in 1929, a short time after this hand-colored photo (now in the Gene Autry Museum) was made.
My wife's great-grandfather leased and operated the original Mammoth claims during the 1930s, part of an operation incorporated as the Mammoth Consolidated Mining Company. Relics of that operation are on exhibit today as a historical attraction— Read about it on my "About the Artist" page.
I used the diagram at right, from Eliot Lord's 1883 Comstock Mining and Miners, as a guide for my model. Rock breaker is on the right, then stamps, amalgamation plates and collecting tank, then pans, settlers, and agitators.
Here's where the process starts— ore is wheeled over the trestle from the tunnels to the top of the mill. Other needed supplies— salt and mercury for the amalgamation process, and wood for the boiler— are brought in by rail.
A mill like this burns a few cords of wood per day. (There's about 4 cords stacked outside.) Eastern California's Bodie & Benton RR existed solely to bring wood to the mines and mills.
The "ore" is real— taken from the site of my wife's great-grandfather's mine. The mine cart is from Durango Press.
The ore is dumped from the cart through a grate of iron bars— a "grizzly". Any oversized rock is fed into the Blake crusher and broken down to size.
More modern mills (1890s–on) had automatic belt-driven feeders for the stamps. My 1870s-80s pan mill still uses guys with shovels.
My mill has 20 stamps. A gap at the end of the batteries makes it apparent there was at one time 10 more. The iron parts of the 10-stamp batteries were made from styrene and brass wire, with Grandt Line wheels and NBW castings.
After the ore had been stamped to fine sand, it was washed over amalgamation plates— copper plates impregnated with mercury— which siezed the particles of free gold. The amalgam was scraped off the plates and taken to an assay lab where the mercury was boiled off in a retort, leaving the precious metal behind.
Gold and silver that was chemically bound up in sulphur compounds— sulphurets— would not amalgamate so easily and needed further processing in the pans to separate the metal from the rock.
The "wet" in the model is acrylic gloss medium mixed with real powdered mine tailings.
The mill is powered by a steam engine— again, built with brass and styrene odds and ends using reference from old mining books and catalogs. The water pump was salvaged from an old Rivarossi Bowker locomotive. The mill's belting and water piping systems are complete and took a lot of planning before construction— a lot of the shafting and piping runs under floors.
I built this model sometime around 1984-85 and intended to make it the centerpiece for a small narrow-gauge shelf layout inspired by the Bodie & Benton RR. The layout never happened. I got sidetracked by an overwhelming interest in the Colorado narrow gauge scene. My Mammoth Mill was boxed away, nearly forgotten, until recently when I got curious about what was in the box marked "Mill" . . . I really should go digging in the garage more often.
The gold or silver ore was shoveled into amalgamation pans where, mixed with water and several hundred pounds of salt and mercury, it was crushed further between "mullers," rotating iron plates. The heavy amalgam collected at the bottom, where they would be periodically cleaned out.
The "slimes"— basically, muddy water from the pans, were run off into settling pans and agitation tanks, where the remaining particles of heavy ore were allowed to separate and settle.
Diagram from Pan Amalgamation of Silver Ores In Nevada and Colorado, by T. Egleston, 1879.
The pans, settlers, and agitators were built up from short lengths of brass tubing and styrene. Also lots of repurposed Precision Scale brake wheels in various sizes.
I raided the Grandt Line and Precision Scale catalogs for wheels. Most are brake wheels and cable sheaves from several different scales. Belt wheels got new styrene rims. The belts are chart tape.
Photo courtesy the Autry National Center
Click on pix for full-sized images.
