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Before a gold dredge could work the frozen gravel of Coal Creek, in what is now Yukon-Charley Rivers National Preserve, somebody had to melt it. In 1935 the operating company tried steam. The thawed ground froze again over the winter, and the company's first operating report judged the work worse than useless and too expensive to repeat. Cold water pumped through pipes into the ground did the job, and the method soon spread to the goldfields around Fairbanks. Douglas Beckstead, who worked for the National Park Service in Alaska, tells the story.
Why gold collects where it does
Gold deposits come in two forms: hard rock, where veins run into the surrounding host rock, and placer deposits, where gold-bearing rock has eroded and been carried some distance. Gold has a specific gravity of 19.32, higher than lead (11.340), silver (10.490), copper (8.940) or iron (7.850), so in moving water it works its way to the bottom and collects where bedrock meets the alluvial gravel. Placer miners remove the overburden to expose that gravel and run it over a sluice, where flowing water lets the heavy gold sink behind riffles while lighter rock and sand wash away. A gold dredge mechanizes the whole job: a chain of buckets scoops gravel into a hopper, water carries it through a trammel that separates the largest rocks from the sand, and sluices recover the gold from the finer material. Dredges worked at various times on Coal Creek and Woodchopper Creek.
Stacked hydraulic hoses at the Coal Creek pipe yard, which carried water from the pipes to the cold-water points; a 2011 wildfire burned the valley and embers ignited the pile of old rubber hoses, destroying them (NPS photo, 1995).
Ground like concrete
Alaska's climate adds a step before dredging. At Coal Creek and Woodchopper Creek, bulldozer operators first stripped away the trees, brush and tundra that formed an insulating blanket, exposing a shiny black surface of frozen muck between 6 and 26 feet deep. That permafrost was as resistant to bulldozers as reinforced concrete.
Steam, then cold water
| Steam thawing, 1935 | Cold-water thawing, from 1936 | |
|---|---|---|
| How it worked | Hardened chisel points on pipes connected to high-pressure steam hoses were driven into the permafrost, and steam escaping at the tip thawed the gravel around it | Heavy-gauge pipes 10 feet long, each with a hardened chisel welded on, were driven down with a slide hammer while water under pressure flowed through and seeped out through two holes on either side of the point; the points went deeper as the ground thawed |
| What it needed | About 250 cords of wood, cut and stockpiled over the winter of 1935-36 to fire a 40-horsepower boiler | Cold water from the ditch high above the creek, run through penstocks and ever smaller pipes to raise the pressure, and controlled by gate valves |
| Result | The dredge struck ground that had re-frozen over the winter. The thawed area was 18,000 cubic yards at 34 cents per yard, and the first annual report said steam thawing would not be tried again | Enough ground thawed to start dredging by mid-July, and the dredge was never bothered by frost in water-thawed gravel. It was the first use in the Eagle-Circle mining district, and the practice soon spread to the Fairbanks goldfields |
Cold water collected in penstocks on the ditch high above Coal Creek and ran downhill through ever smaller pipes, which raised the pressure; gate valves controlled it before it flowed out to the points in the thaw field ahead of the dredge (NPS photo, 1995).
Patty, who wrote the company's operating reports, estimated that the water entered the pipes at about 45 degrees Fahrenheit and left the ground around the points at about 35, so it passed roughly 10 degrees of heat to the gravel at minimal cost. Thawing had been left to the dredgemaster, Fred Obermiller, who had years of experience with similar operations at the Fairbanks Exploration Company. When the dredge first worked steam-thawed ground, early reports called conditions nearly perfect, an optimism that ended when it hit the re-frozen patch.
The 1936 season did not run smoothly. The first 250 cold-water points went in on May 18 and within two weeks all had reached bedrock. A further 250 were on hand, but the flanged feeder pipe to supply them was due on the first down-river boat from Whitehorse on June 5, and the White Pass & Yukon Route failed to load it despite arrangements made months earlier. The pipe went on the steamer Klondike, which sank. A duplicate order arrived in late July, some of the original was salvaged, an additional order of points came in August, and a final order of 250 for 1937 arrived late in the season, giving the company nearly 1,000 points, most of which are still in the Coal Creek pipe yard. With too little ground thawed ahead of it, the dredge shut down on October 5, 1936, a full month early. The company kept careful records so others could repeat the method.
Cold-water thaw points and valves at the Coal Creek pipe yard; the long sections of pipe in the background are the thaw points, each with a hardened steel chisel point welded to one end and threads on the other (NPS photo, 1995).
Where did the fuel barrels go?
The economics of dredging explain a puzzle. In the mid-1990s the Park Service gathered abandoned drums from the Coal Creek drainage for recycling and was surprised to find no old barrels: nearly all dated from the late 1960s and 1970s. How could an operation that ran from 1935 to 1960 leave none scattered about?
The answer was the deposit on barrels. Early on, barges carried full barrels down the Yukon from Whitehorse and brought empties back to be refilled, which was no great hardship. Between 1942 and 1946 operating costs rose approximately 26 percent while gold held at $32.00 an ounce, so the company hunted for savings, and one was to stop paying barrel deposits. It built a large oil tank high on the bank of the Yukon slightly downstream from Slaven's Roadhouse; the piping is still visible. Fuel came down the river in a tank on a barge and was pumped up to the holding tank. When the camp needed fuel, a tractor pulled the Athey wagon, the large tracked wagon that still stands at Coal Creek Camp, down to the river to fill a smaller tank, which was hauled to the dredge and tractors. All the empty barrels from the earlier years were shipped back to Whitehorse and the deposits refunded. As inflation kept rising and the price of gold did not, management kept trimming costs. By the 1960 season its board decided to close the operation for good, and the crew cleaned up and left in October 1960.
Sources
- Douglas Beckstead (National Park Service), Fire vs Ice: Revolutionizing the thawing process at Coal Creek, Alaska Park Science, Volume 13, Issue 2; rewritten in hubnx's own words.
In these publicationsYukon - Charley Rivers National Preserve
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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