|MadSci Network: Earth Sciences|
There is no special gold-finding device, like there is for radioactive materials. However, there are many ways of prospecting for gold, some of which include the use of sophisticated devices that can also be used for other purposes. One of the oldest methods is still a good first step: panning. Gold is refractory, which means that it is not easily destroyed. Therefore, when gold-bearing rocks weather, the gold particles are transported more or less intact and end up in streams. Because gold is heavy it is concentrated with other heavy particles in places where light particles cannot settle. Panning carries this process a step further and allows gold to be concentrated in a pan from which lighter materials have been winnowed (washed out). If you find gold in a stream, you have already located one gold deposit, but you do not know the size and shape of the area in which gold can be found. Also, the gold in the stream bed must have a source, and the particles of gold in the stream are a clue to this unknown source, which could be more valuable than the auriferous (gold-bearing) stream sediments. You can follow the gold downstream until it is so rare that it is not worth seeking, and you can follow it upstream, towards the source. When the gold in the stream vanishes, you have passed the source. The gold in a stream is commonly derived from rocks formed by hydrothermal (hot water) activity. Hydrothermal quartz crystals fill fractures in rock (forming quartz veins) and sometimes gold is deposited with the quartz. This is not the only kind of rock that contains gold, but it is one of the most common. If you know from panning that there is a source of gold in a certain region, you can search for it in several ways. Wandering around with a burro and a hammer can work, but some modern methods are more effective. You can look for hydrothermal rocks, or the other kinds of rocks that may harbor gold. When you find them, collect samples and have them analyzed chemically. In this way, you can find concentrations of tiny gold particles that you might never see with the naked eye. If you find that the gold is indeed in a hydrothermal deposit, then knowledge of how and where that deposit formed gives you more clues about where to find the gold. Generally, the geologic history of a region dictates that a given type of deposit (for example, hydrothermal quartz veins) can form only in certain places. Thus, you can prospect for gold using a geologic map. Modern prospectors may use a variety of methods: knowledge of historical discoveries, chemical analyses of rocks that could host gold, geologic mapping, and so on. After the gold deposit is located, additional chemical analyses are needed to determine how much gold is present and the concentration of gold in the ore. If the deposit is small, or the ore of low grade, it might cost more to mine the gold than the metal is worth. I hope this brief summary helps. I urge you to go online and look for other sources of information about gold. Here is a link to a list of earth-science education web sites (http://www.gsa.state.al.us/gsa/Education/edpglnk3.html). There is a section listing web sites that give minerals information where you can learn a lot more about gold and about mining. David Kopaska-Merkel Geological Survey of Alabama PO Box 869999 Tuscaloosa AL 35486-6999 (205) 349-2852 fax (205) 349-2861 www.gsa.state.al.us
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