The early prospectors who came to the Yukon had a number of challenges to overcome, some of them unique to the North. But the most peculiar and northern of conditions that they confronted was permafrost.
Permafrost is a condition found in the Far North where the ground, a few centimetres from the surface, remains frozen year round – and has done so for thousands of years. Permafrost ground, when first encountered, can be rock hard, but if disturbed can quickly be converted into a quaking quagmire. This was a major obstacle that confronted the engineers who had to construct the Alaska Highway!
The earliest of the prospectors who entered the Yukon 15 years before the Klondike gold rush did not know where the gold was – they had to search it out. They hauled their supplies from Juneau, over the Chilkoot Pass and spent the summer hunting for the elusive pay streak. Thus, the effectiveness of the early prospecting was limited by the amount of time that they had left over after accounting for the time required to travel to and from the Yukon valley.
They quickly learned about permafrost. Their earliest prospecting efforts were concentrated along the banks and bars of the Yukon River and its tributaries. In bar mining, the miner repeatedly scraped away the loose material and thus allowed the ground to thaw down a few centimetres at a time. They were limited by the water level of the river, the depth of the permafrost along the banks, and the amount of gravel they could move by hand.
Within a few years, prospectors started camping in the interior of the Yukon during the winters. This allowed them to extend their prospecting season in the spring and fall. But these men spent their winters hunting for food and waiting idly until spring. They couldn’t prospect while the ground was frozen and covered with snow.
The first recorded instance of thawing being employed was in 1882, by Jack McQuesten, Joe Ladue, and others on the Sixtymile River, but when the thawing method was perfected is unclear. By the 1890s it was in common use in the Fortymile district.
Where the overburden was deep enough, around five metres down or more, fires were set on a selected location and, as the ground thawed, it was excavated before it could freeze again. Another fire would then be set and the excavation continued until bedrock was reached. The frozen ground was as hard as granite, so it did not require cribbing to give it support.
Once on bedrock they dug horizontal tunnels, or drifts, usually at right angles to the valley hoping to intercept the pay streak, which would be excavated and followed. The material removed from this zone was stockpiled in a dump on the surface until the warm weather when the gold could be sluiced out using spring run-off.
This was called drift mining and it allowed the prospectors to remain busy all year round.
Once gold was discovered in the Klondike and the richness of the ground was proven, the miners started to import steam equipment – such as pumps, steam engines and hoists, to excavate and sluice the gold more efficiently, and maximize the profitability of their claims.
One day, Clarence Berry, a successful miner on Eldorado Creek, observed that steam exhausted from a steam engine was thawing the ground nearby. It is said that he conceived the steam-thawing point by sticking a gun barrel on the end of a steam hose, and forcing it in the ground. As the ground thawed, the point was driven farther and farther into the ground until the desired depth of thawed material was achieved.
Soon all the miners were using specially designed steam points that could be hammered farther into the ground as the steam softened the permafrost. Within a decade, this was a common practice for thawing the ground ahead of an advancing dredge, and immense networks of hundreds of steam points were laid out to systematically thaw the ground.
Steam thawing proved to be a costly venture, and it was replaced within a decade or so by cold-water thawing, a technique developed in Nome, Alaska, around 1918. Thawing with cold water was cheaper, and the pattern of thawing underground was more thorough, thus creating a more consistent zone of ground for the dredges to eat up.
Combining the lower cost of cold water thawing with the increased price for gold after 1934, the Yukon Consolidated Gold Corporation expanded its fleet of dredges and continued to operate in the Klondike until 1966.
With end of the dredging era, other methods of mining came into common use, most notably the use of tracked bulldozers, or “cat” mining, but miners still have to contend with permafrost. Each miner has conditions unique to their circumstances. The nature of the ground, the exposure to sunlight, topography and other factors are all considered when selecting a method to thaw the ground.
In broad exposed areas, the ground can be stripped over a large extent of terrain and then scraped away as it is thawed by the sun, just like the early miners did by hand along the river bars. Hydraulic monitors are often employed to wash away the frozen overburden and muck to get down to the paying deposits below. Ground sluicing, diverting water into desired areas and allowing the natural flow thaw the ground, has also been employed.
Caterpillar tractors are now equipped with a ripper, which is a giant steel tooth mounted on the back end which can be forced down into the ground and then dragged, thus breaking up the frozen component, making it easier for thawing to occur. Of course, this is hard on equipment and results in costly wear and tear.
Both dredge mining and the more recent “Cat” mining move ground in volumes that the early prospectors couldn’t have dreamed of
Bern Johnson, who mines with his brother Ron on the tributaries of Eldorado Creek, recently described to me the use of explosives to break up the ice-locked gravels in steep, narrow gulches where they mined, and where the ground is shaded from the sun’s warming effects.
I can remember the 1980s, when blasting was employed on a mining operation on Jackson Hill in the Klondike Valley, not far from Dawson. Every time a charge of explosive was set off, the windows in our home rattled from the concussion.
Overcoming the permanently frozen ground has always been a challenge to miners’ creativity. With the allure of gold to stimulate their ingenuity, they have found many ways to solve the problem. I wonder if climate change will do away with permafrost making these innovations unnecessary?
Michael Gates is a Yukon historian and sometimes adventurer based in Whitehorse. His latest book, History Hunting in the Yukon, is now available. You can contact him at firstname.lastname@example.org