Mining Mining • Minerals are naturally occurring substances found in rocks, soils, or sediments. • Minerals deposits that can be mined profitably are called ores. • They can be either metallic or non-metallic Minerals can be classified into 4 categories. 1. Metallic minerals – Associated with intrusive igneous rock – These deposits can consist of valuable metals such as nickel, copper , zinc , lead, and gold – Metallic minerals must be broken apart and chemically processed to extract the useful metal from the mineral. – At one time magma containing dispersed minerals was forced up towards the earth’s surface through fissures. • Super heated brines dissolved metallic elements, which flowed into some of these cracks. As they cooled they solidified and formed veins. Veins of gold 2. Fuel minerals - Found in sedimentary rock - formed from the remains of living organisms that were transformed over time by heat and pressure into coal, oil, or natural gas. 3. Industrial minerals (gypsum, potash, rock salt) - found mainly in sedimentary rock. - formed in shallow seas in regions with hot dry climates. - as water evaporated, it became more and more salty - eventually the salt began to build up in layers - in some cases the seas dried up . 4. Structural minerals - associated with all types of rocks - are the products of river, wind, and glacial deposition - include sand, gravel, and clay - used mostly as construction materials Finding a deposit • The old fashioned way of finding a mine was your prospector with a pick and shovel, a gold pan, and a lot of luck. • Today, technologies used include, but are not limited to, exploration geology, geophysics, geochemistry, and satellite imagery. Geology • Geology is the study of the planet Earth— the materials of which our planet is made, the processes that act on these materials, and the products formed. • Geologists use ground-mapping techniques to identify features seen on satellite images and aerial maps of large tracts of the continent. Satellite Imagery • Ground-based surveys are expensive, and one can often experience difficulty in mapping large-scale structures. However, large geological structures are often readily visible on satellite imagery. Geophysics • Geophysical exploration involves searching for favorable mineral deposits using the physical properties of rocks. • Geophysical investigations groundpenetrating radar studies or the use of seismic waves to show contrasting rock types. • The selected rock units of interest might then be mapped and sampled. Geochemistry • Geochemists can determine the composition of what lies below the Earth's surface by sampling soil. Soil at the surface can carry a chemical signature of what lies below, because of the movement of chemicals through the rise and fall of the water table. • Positive geochemical results from surface sampling are followed by a drilling program. Because of the great expense, drilling is only carried out when the area is very likely to contain substantial mineral deposits. • Drilling produces either rock fragments, or 'cores' of rock for sampling to determine whether the mineral deposit contains worthwhile concentrations of ore minerals. • • • • Types of Mines 1. Open pit Used when ore bodies lie near the surface Large hole exposes the ore body Waste rock (overburden) is removed 2nd cheapest method, but has the largest environmental impact. Why? 2. Strip Mining • The cheapest and safest method, but can have a significant impact environmentally on the surface. Why? • The ore is close to the surface of the land (30m) but has one or more layers of rock and dirt on top of it. To mine the ore, these layers have to be taken off. • This mining is done in long, narrow strips. When the ore is done in one strip, the miners begin to create another strip next to it. The waste, dirt, and rock that they take off of the top of the next strip is put on top of the last one. 3. Underground Mining • Very expensive and the most dangerous of the three methods, but has the least impact environmentally on the earth’s surface. Why? • Underground mining is done when the rocks, minerals, or gemstones are too far underground to get out with surface mining. • Entry into underground mines is by vertical shafts, or by a sloping tunnel.