Drift mining

Drift mining is a method of accessing valuable geological material, such as coal, by cutting into the side of the earth, rather than tunneling straight downwards (see shaft mine). Drift mines have horizontal entries, called adits, into the mineral deposit from a hillside. Drift mines are distinct from slope mines, which have an inclined entrance from the surface to the mineral deposit. If possible, though, drifts are driven at just a slight incline so that removal of material can be assisted by gravity.

Nome Alaska
Drift mining methods were used extensively during the gold rush, around the turn of the last century, in Nome, Alaska. The technique, slightly different than that described above, was ingeniously adapted to the challenges faced in the region. Gold was abundant around the turn of the century in Nome. During the warm summer months gold could be easily recovered using gravity separation techniques; these techniques required water.

It didn't take long for miners to discover and recover all of the "easy" gold. During the winter time, when the sun disappears for months and everything including the ocean freezes, miners found themselves sitting around in bars doing nothing, or drinking and getting in trouble. Most of the ground in Nome, called permafrost, has been frozen solid for centuries. By "drift mining" miners were able to recover much of the gold buried under the permafrost, as described below.



Gold is not everywhere, over time nature causes it to be concentrated in specific places. In Nome these places included three ancient beach lines, now inshore, above sea level, and buried under roughly fifty feet of permafrost with two feet of tundra (a mossy layer of vegetation that acts like a blanket to keep the permafrost frozen during the summer) on top of it. The miners that drifted these buried deposits got rich beyond your wildest dreams!

The first step in mining is, of course, finding the gold. This is called prospecting. Drift miners, knowing roughly where to look, still had to find exactly where the gold was deep under the frozen ground. This was done by building a fire on top of the permafrost and, each day as it melted, shoveling away the mud. The process would be continued until reaching either a "pay streak" or bedrock. Not all prospecting shafts paid off. Even the luckiest miners prospected many a barren hole before striking it rich. When the gold was found the true "drift mining" began.

Gold, when it was finally found in these places, occurred on top of either bedrock or "false bedrock" (a layer of clay that the gold was not able to sink through). Drift miners, once they had found a "pay streak," would tunnel horizontally from the bottom of their prospecting shaft and follow the gold across the surface of the bedrock. This was a very efficient mining method. The fifty feet or more of frozen dirt above them did not need to be removed. The tunnels, because the ground was frozen, would not cave in. Miners would discover old underground beaches and rivers rich with gold and follow the gold until it was depleted. One drift miner, on "Little Creek" in Nome, having sunk five unproductive holes, almost out of money, and working on his sixth, struck what turned out to be the richest pay dirt ever found on the face of the planet; two hundred ounces of gold per pan (a small shovel full of dirt). Around the year 1900 the population of Nome was more than twenty thousand; it's a bit less than four thousand today. Many of those people were drift miners. Nome's gold fields, appearing untouched from the surface, are honeycombed with tunnels left by the gold rush drift miners. Today's miners, as they prospect for gold using modern drilling equipment, almost expect as they follow promising underground signs of gold to find, right when they think they're going to strike it rich, that a gold rush era drift miner has beat them to it! Their drill, grinding through the permafrost, suddenly hits an air pocket... a drift miner's tunnel.

Today's miners use heavy equipment to remove all of the dirt, or "overburden" from on top of the pay streak. With all of the "easy" gold long gone, this takes a lot of digging. A personal friend, after spending two years digging a huge pit with excavators, was dismayed to find a drift miner had been there first; there was other gold, but the drift miner had gotten the best of it. This form of drift mining proved to be an efficient and safe way for turn of the century miners to recover gold from deep beneath the frozen ground in Nome Alaska. It could be done during the winter. A hot fire, some shovels, and a few hearty souls were all that was needed. To their credit, for their hard work and persistence, many a drift miner left Nome with pockets full of gold.

From http://en.wikipedia.org/