Drift mining
Encyclopedia
Drift mining is either the mining of a placer deposit
by underground methods, or the working of coal seams accessed by adit
s driven into the surface outcrop of the coal bed. Drift is a more general mining term, meaning a near-horizontal passageway in a mine, following the bed (of coal, for instance) or vein of ore. A drift may or may not intersect the ground surface. This kind of mining is done when the rock or mineral is on the side of a hill.
. During summer, surface deposits could be worked, but some placer deposits were buried too deeply for surface placering. In addition, water to wash the gold from the placers was not available in the winter. Many miners tunnelled into deep placer deposits, bringing out the high-grade gravels to be washed at the spring thaw. Most of the ground in Nome is permafrost
. By drift mining, miners were able to recover much of the gold buried under the permafrost.
Gold at Nome was concentrated in three ancient beach lines, now inshore, above sea level, and buried under roughly fifty feet of permafrost overlain by two feet of tundra
. Gold was usually found on top of either bedrock or "false bedrock," a layer of clay that occurred at the base of the beach or stream deposit.
The miners initially sank shafts to prospect for the pay streaks. This was done by building a fire atop the permafrost, and, each day as it melted, shovelling away the mud. The process would be continued down to either a pay streak or bedrock. When the gold was found, the drift mining began.
Once they had found a pay streak, miners would tunnel horizontally from the bottom of their prospect shaft, and follow the gold along the surface of the bedrock. The tunnels, because the ground was frozen, would not cave in. Miners discovered old underground beach and river gravels rich with gold. Around 1900 the population of Nome was more than twenty thousand, many of them 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, prospecting with modern drilling equipment, sometimes hit old drifts.
Placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early...
by underground methods, or the working of coal seams accessed by adit
Adit
An adit is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, and ventilated.-Construction:...
s driven into the surface outcrop of the coal bed. Drift is a more general mining term, meaning a near-horizontal passageway in a mine, following the bed (of coal, for instance) or vein of ore. A drift may or may not intersect the ground surface. This kind of mining is done when the rock or mineral is on the side of a hill.
Nome, Alaska
Drift mining methods were used extensively to mine placer deposits during the early years of the Nome mining districtNome mining district
The Nome mining district, also known as the Cape Nome mining district, is a gold mining district in the U.S. state of Alaska. It was discovered in 1898 when Erik Lindblom, Jafet Lindeberg and John Brynteson, the "Three Lucky Swedes" , found placer gold deposits on Anvil Creek and on the Snake...
. During summer, surface deposits could be worked, but some placer deposits were buried too deeply for surface placering. In addition, water to wash the gold from the placers was not available in the winter. Many miners tunnelled into deep placer deposits, bringing out the high-grade gravels to be washed at the spring thaw. Most of the ground in Nome is permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
. By drift mining, miners were able to recover much of the gold buried under the permafrost.
Gold at Nome was concentrated in three ancient beach lines, now inshore, above sea level, and buried under roughly fifty feet of permafrost overlain by two feet of tundra
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
. Gold was usually found on top of either bedrock or "false bedrock," a layer of clay that occurred at the base of the beach or stream deposit.
The miners initially sank shafts to prospect for the pay streaks. This was done by building a fire atop the permafrost, and, each day as it melted, shovelling away the mud. The process would be continued down to either a pay streak or bedrock. When the gold was found, the drift mining began.
Once they had found a pay streak, miners would tunnel horizontally from the bottom of their prospect shaft, and follow the gold along the surface of the bedrock. The tunnels, because the ground was frozen, would not cave in. Miners discovered old underground beach and river gravels rich with gold. Around 1900 the population of Nome was more than twenty thousand, many of them 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, prospecting with modern drilling equipment, sometimes hit old drifts.