Placer mining is a kind of surface, open-pit mining. When you think of this kind of mining, you usually think of early Gold Rush prospectors. Click here to visit our Prospecting page.
Prospectors, another name for miners, were looking for gold. They might find it in flakes, nuggets, or gold dust. Gold is found in veins like the ones in the palm of your hand. The gold had to be separated from the rock around it. Sometimes water erosion helped it along by wearing away the rock so that the gold flowed with the water into the nearby rivers. When this happened, it would travel with the water until it reached parts of the river where the water slowed down—like bends in the river. Because gold is heavier, it would drop to the bottom. This was a terrific thing for the early prospectors because it took an underground mineral and made it into a surface mineral. Surface minerals are easier and cheaper to reach. Prospectors would travel around until they found their claim, or land that they wanted to mine.
Placer mining was done in rivers, creeks, and streams. The great thing about placer mining was that you didn’t actually have to know too much about mining to do it. Simply said, placer mining was where the miner scooped dirt into a pan from the bottom of a stream, river, or creek. He swirled the dirt and water and then poured the water out of the pan [panning]. Since gold was heavier, it would be left in the pan. That’s why miners used to say that they hit “pay dirt” when they found lots of gold in one place.
If the prospector found a stream where there were lots of gold nuggets, he used a rocker. Rockers were long boxes that the prospector shoveled the dirt and water into. He would rock this box [like panning], combining the water and dirt, and this poured out the end of the box leaving the gold behind. Sometimes placer miners would work together because this made the job easier. It was not an easy job. Miners stood in cold, deep water for hours and hours and the work was really hard.
| The picture on the right shows a sluice taking the water, dirt, and gold downhill. A geological engineer, named Rafal Swiecki, says that even expensive new tools for dredging gold don’t work as well as the sluice. He says that the sluice doesn’t clog up as much as the newer equipment does, it is cheaper, and actually collects more gold the first time through. It is interesting to see that placer mining is still going on all over the world. | |
Surface placer mining has its drawbacks, though. The streams and rivers that are being mined have their bottom layers removed. This wrecks the habitats that were down there. The environment is hurt by the sandy silt that flows down into other streams from the mine. This changes the level of the streams and makes them muddy so that the sun doesn’t reach the fish and underwater life.
TODAY'S PROSPECTING:
We thought that prospecting was over with the Gold Rush. We were surprised to find out that it isn’t true. Nowadays, prospectors are usually looking for underground minerals because—like in the Gold Rush days—surface mining has already found the minerals that are on, or close to, the surface. Satellite photos are used to find places where minerals might be located. The gold rush prospectors went from river to river until they found gold. This took a lot of time and was mostly unsuccessful. Now we use scientific tools to test the ground above areas that might be mined. Scientists look for something called ‘trace elements’ which are really small pieces of rocks or ore that tell the scientists that the mineral might be there. For example, when we visited the zinc mine, we were told that it was originally found by people who saw zinc ore on the top of the mountain. Geologists knew what kind of rock would be found around zinc ore so they probably looked for that, too. With the high cost of underground mining, scientists are sure to locate a mineral, find out how much is there, and test the quality of it before they ever begin to mine it.
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