Prospecting is the process of searching for valuable deposits of minerals or fuels. Early prospectors in the United States were lured by the promise of gold, oil, and other valuable minerals. Gold prospectors explored deep canyons and high mountains with picks, shovels, gold-pans, and other simple equipment. Petroleum prospectors drilled shallow holes looking for oil reservoirs. Most early prospectors had no scientific training. Modern prospectors, sometimes called explorationists, are scientists with extensive training in geology, geophysics, and mining.
Prospectors today mainly search for deeply buried deposits, because most minerals that were near the surface have already been discovered. They usually begin by examining areas of known deposits to determine the conditions under which valuable minerals or fuels occur. Using satellite photographs of Earth’s surface, prospectors choose a site whose surface conditions indicate the likely presence of minerals underground.
To learn what lies underground, prospectors have the site’s topsoil, water, and plants analyzed for trace elements. Trace elements are extremely small amounts of certain chemical elements. Their presence in topsoil, water, and plants may indicate deposits of a certain mineral below the surface.
Prospectors use several instruments in their search for deposits. Gravimeters, or gravity meters, measure the pull of gravity at Earth’s surface. Metals and other dense rocks increase gravitational pull while light, porous minerals decrease it. Magnetometers record changes in Earth’s magnetic field. Magnetometers help prospectors find petroleum, certain iron ores, and other minerals with magnetic properties. Prospectors use lamps that give off ultraviolet light to find fluorescent minerals. When illuminated with this light, these minerals glow with definite colors. Geiger counters and scintillation counters measure radiation. Prospectors use them to find radioactive minerals such as uranium and thorium. Seismographs measure movements of Earth’s rock, such as shaking produced by earthquakes or vibrations created by underground sound waves. In the seismic method of exploration, prospectors use explosives to create sound waves. By studying the speed and direction of waves reflected by buried rock layers, prospectors can determine the structure of the layers.
Once prospectors have determined that a site contains valuable minerals, they drill deep holes at the site to obtain rock cores or fragments. These samples help the prospectors determine the size, value, and exact location of the deposit.
