Mining

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Success in mining, like any business, requires that the minerals extracted by a mine produce more value over its operating life than was consumed in developing and operating it. Prospecting, mining and processing minerals are complex processes that cost significant amounts of money to undertake. Although the return on a mining investment can be high, it can also be highly uncertain.

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Rocks are composed of minerals. Each of the thousands of minerals found in the earth’s crust contains a specific combination of elements in specific proportions. Although some elements can be found in an almost pure form (gold or copper, for example), most are chemically bound up in minerals. Human societies have come to value particular elements and minerals more than others, for use as fuels, to make tools and chemicals, or to wear as jewellery. We have also learned to recognize these elements and the minerals that contain them in the rocks that make up the surface of the earth.

Valuable minerals are found throughout the earth’s crust, but the cost of extracting and purifying a particular mineral from the average rock is far greater than the value of that recovered mineral. The first step in mining is therefore to find the valuable minerals in a sufficient concentration, compared to the average rock, that they can be recovered profitably. The term ore is given to rock containing an economically significant quantity of a valuable mineral.

To find ore, geologists map the geological features of an area, examining the surface materials and underlying rocks for indications of valuable minerals. Modern prospecting uses a variety of airborne remote-sensing technologies (for example, images from satellites and measurements of the magnetic properties of rocks from aircraft) to help identify areas that are considered likely to host such a concentration. Remote sensing can cover large areas fairly quickly compared to walking the land, but it is costly and requires careful analysis to be useful. The area indicated by remote methods must still be confirmed by people on the ground to directly examine the area and sample the mineral content of the rocks.

If fieldwork confirms a promising site, the bedrock is exposed to allow the mineralized zone to be explored using drills. Diamond-tipped drills remove a long cylindrical core of rock that is used to determine an approximate size and shape of the ore zone. Many holes are drilled and, as each one intersects the ore, it helps build up a three-dimensional picture of how the ore is distributed through the surrounding rock. Samples are collected from these drill cores and analyzed to determine the various concentrations of valuable minerals across the orebody.

The three-dimensional shape and size of an orebody within the rock determine the methods of accessing the ore and the costs of removing it. The size and shape of a particular orebody, combined with the concentration of minerals in the ore, determine its potential value. The potential value is then compared to the cost of prospecting, mining and processing the ore to determine if it is economically feasible to actually mine the orebody.

The grade of an orebody is an average measure of the amount of valuable mineral contained in each amount of worthless rock. It can be expressed as a percentage or as a ratio (for example, ounces per ton or grams per tonne). It is a complex calculation because the concentration of minerals varies across the entire orebody. It is also a crucial number to get right, as it is the basis for determining how valuable an orebody is. Low-grade orebodies may still be profitable to mine, but larger amounts of ore must be mined for it to be profitable.

Once the decision to mine has been made, facilities must be built to bring the ore to the surface and prepare it for the extraction of its valuable content. Ore found deep beneath the surface is accessed by shafts or ramps cut into the rock. In this case, all mining activity occurs underground using a series of tunnels to access and haul the ore to the surface. An open-pit method can be used to access an orebody located near the surface. The ore is removed in a series of concentric holes dug into the rock, each deeper and smaller than the previous one.

Once the ore has been mined, it is crushed and processed in order to concentrate the valuable minerals and remove the worthless ones. The exact method used depends on the type of mineral being treated. This ground mineral concentrate must then be sent to a a smelter or refinery in order to produce a final product suitable for commercial or industrial use.

Dealing with the material left over once the valuable minerals have been removed is a major challenge in mining. Waste rock may contain chemicals from the mining process or naturally occurring minerals in concentrations that can pollute the environment if not stored or treated properly. Underground mines often combine crushed rock with concrete and use it to refill areas that have already been mined.

Even when an orebody is considered profitable enough to mine, there are still considerable economic risks that can occur over the operating lifetime of the mine. Events that can affect the profitability of a mining investment include changes in interest, currency exchange and taxation rates; changes in the price of commodities used in mining; changes in demand for mineral products; and changes in the regulations under which mines operate. Each of these events can force mining activity to stop until economic conditions improve, allow an unprofitable orebody to be mined or allow a mine to reopen.