Tuesday, October 25, 2011

Depth Matters: A Tour of the Kennedy Mine Property in California's Mother Lode

We took one of our fall semester field studies trips last Saturday, to the California Mother Lode between Jackson and Columbia. It included a tour of a spectacular marble cavern (in a coming post), and the Kennedy Mine, which for a long time was one of the most important gold mines in the state.

The mine was the subject of my last post, a first impression of some of the info I learned during the tour: how people died working underground. The tour at the mine was conducted by volunteers working with the Kennedy Mine Foundation, a non-profit organization, and our guide was a fountain of information. The tour is above ground, as the mine was vertical for hundreds of feet, and flooded to boot. Our tour actually lasted 40 minutes longer than the scheduled 90 minutes, which caused me a bit of stress as I was watching the clock ticking towards the appointment time for our other scheduled tour! It was a great opportunity to see one of the most important mines of the Mother Lode.

The grounds are heavily overgrown with gray pine and oak trees, and the site is actually preserved as open space for wildlife (the wishes of the last owner of the land). This was quite a contrast to the old days; a look at old photographs indicated that the site was actually pretty barren of vegetation during the mining years.
The headframe will last a long time. It is 135 feet tall, and composed of iron beams. The original 100 foot tall wooden headframe burned (along with most of the surface developments) in 1928. Debris from the burning headframe fell down the main shaft, blocking any chance of exit for the miners still working thousands of feet below. A previous tragedy saved the men's lives: in 1922 the adjacent Argonaut Mine had burned and 47 miners died. In the aftermath, a connecting tunnel was left in place at the 4,600 foot depth between the two mines. This tunnel allowed the miners to escape unharmed.
The building in the picture at the top of this was the changing room, where miners coming off their shift could shower and change cloths before going home. It serves today as a museum and gift shop. The showers weren't really a job benefit...it allowed the mine operators to make sure no one was walking home with gold samples in their pockets! The practice, called high grading, was a constant problem for the mining companies (maybe if they paid their workers better?).
The cement monoliths above are the foundations of the main hoists for the mines. Keeping air in the mine breathable required an extensive ventilation system; carbon dioxide is a heavier gas and could often sink to the lower reaches of the mines and cause suffocation. If you remember the phrase "canary in a coal mine", it reflected a truth. Miners would carry canaries, which were more sensitive to bad air than humans. If they stopped singing, miners knew they were in danger.
Ore was hoisted to the surface of the mine, and processed in a stamp mill on the slope below the headframe. The Kennedy Mine had one of the largest stamp mills in the entire Mother Lode, with 100 stamps. Each stamp weighed nearly half a ton, and they were in constant motion, vertical hammers rising and falling, crushing the ore into a sand-like consistency. Mercury and other "benign" chemicals were used to separate the gold from the waste material. Mercury combines with gold to form a solid alloy called amalgam.

The mine waste was a problem. It was full of sulfide minerals that converted to acids on exposure to the atmosphere, and water in the town below was being fouled. In the early 1900s, a system of buckets and giant wheels was constructed to carry tailings over a nearby ridge to a reservoir that could isolate the poisons from the domestic water supply (you can see pictures of the wheels here).
 The monstrous piece of metal in the picture below was a camshaft that was used to lift the stamps.
The mine office is the best preserved building on the mine property. It was built in 1908, and was one of the only buildings to survive the 1928 fire. It included some contradictory operations, although they make a certain amount of sense when one thinks about it. There were two big blast furnaces, one for separating the gold from the mercury, and the second for melting the gold and producing ingots for delivery to the mint in San Francisco. I have to imagine that the whole building must have been terribly hot in summertime (temps in the Mother Lode often exceed 100 degrees). The other side of the ground floor was the assay office, which tested ores at the end of every day, so the quality of ore was always known.
The second floor contained mine offices, the safe, and the pay room. Miners made around $4 a day in the 1920s, and specialists (foremen, carpenter, assayers, and blacksmiths made almost twice as much). These were fairly reasonable wages for the time.
The third floor contained four bedrooms of all things. They were there to house investors when they paid a visit to the mine. They mostly lived in San Francisco and the journey could be long and dusty.
The view from the mine office building is quite nice, overlooking the town of Jackson, and the eroded volcanic neck of Jackson Butte, seen in the picture above.

The Kennedy Mine operated unsuccessfully from 1860 to the late 1870s. New technology (especially the invention of dynamite and steam operated drills) led to a successful expansion of the mine in the 1880s, and the Kennedy operated profitably until 1942 when it is shut down by presidential decree during World War II. When it closed down it was the deepest mine in the United States at 5,912 feet. It ultimately produced about 1.5 million ounces of gold, worth about $2.4 billion at today's prices. It was one of the biggest gold producers in the Mother Lode.
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