Yesterday was spent doing set construction for our upcoming production of You Can’t Take it With You. The spouse of one of the actors is a gold miner and a pretty fair carpenter. He returned early from a placer mining expedition this summer west of Dawson, YT, Canada, across the border on the US side.
My acquaintance- we’ll call him “Ted” because of confidentiality- was a bit reluctant to discuss the recent expedition only because he felt his part in the thing was minor. In fact, his comments were very telling of the kinds of hardships facing anyone with a fancy for placer mining in Alaska or the Yukon Terrritory.
Ted has plenty of experience in placer mining in Colorado, especially in the Fairplay region west of Denver. Placer mining has a special appeal to those who want to mine for gold, but don’t want the grief and expense of underground mining of chemically complex ores.
Ted signed up to work for a New Zealand miner who had a sizeable claim an hour outside of Boundary, AK, along the Top of the World Highway. This site is reasonably remote, judging by the fact the nearest city where machine parts could be obtained was Dawson, across the border in Canada. Mining season is 100 days in duration, or 2400 hours. This is because of the climate and the hardships associated with work out in the bush.
The gold bearing formation is a band of sand and gravel 3-6 ft in thickness and 6 ft below the topsoil. The gold bearing gravels sat atop the bedrock. The miners use a floating separations plant consisting of a trommel and a sluice. The machine had a long elevator with a belt for transferring gravel and rock from the sluicing operation.
The gold is recovered in a densly knapped carpet positioned along the bottom surface of the sluice. The gold particles are trapped in the fibrous mat and are periodically flushed out into centrifuge bowls for further separation.
The operation requires a good deal of readily available water. Ted recounted that the sluice process water was returned to a pond for reuse. The position of this pond had to be managed constantly.
Here is how the operation works. The overburden on the claim must be removed well before the sluicing is to begin. This is done with a D-9 Caterpillar. Owning a large piece of machinery in the wilds of Alaska is an expensive proposition. A small mining operation cannot afford a new Cat, so a used machine must be purchased and delivered. This machine consumes X gallons of diesel per hour and suffers from mechanical breakdowns on occasion.
A small mining operator must be able to do maintenance and repairs because having a mechanic on site may not be possible. The operator must have plenty of working cash on hand to pay for very expensive fuel and parts. Flying parts in will consume much of the short mining season.
The operator must carefully scrape the overburden away to reveal the ore body. Leaving too much overburden will consume extra sluicing plant time. Once the ground is scraped a pond must be constructed in order to support a floating sluice plant.
The sluicing plant is fed by an end-loader or back hoe. The gravel and sands are loaded into a trommel to sort the material and remove the large rock. The finer mesh gravels are then washed onto a sluice where a flow of water will wash the material across riffles to cause deposition of the denser components like gold. Carpet positioned below the riffles will trap the fines and prevent them from being washed away by overexuberant water flows.
Ted said that gold dust recoveries can be as much as 6 ounces per hour when everything was operating smoothly. While this sounds like a lot of money at the current price of gold, bursts of profitable sluicing can easily be overcome with expenses and downtime due to logistical snags, equipment mishaps, and unanticipated difficulties with the deposit itself.
One of the problems that this kind of mining operation can encounter with subsurface deposits in Alaska is the presence of permafrost. Ted explained that his early departure form the site was due to extensive permafrost in the claim. If you cannot dig up the gravel, you cannot recover the gold from it. Like any other single continuous processing train, downtime leads to a cessation of operating capital.
In Ted’s experience this summer, all of the puzzle pieces were in position except for the condition of the gravel deposit. It happened to be frozen in place. It remains to be seen if these operators will return next year.