![]() Heap leaching was used many years ago as a method to recover very low percentages of metal remaining in the tailings from mineral processing plants. A few examples of commodities mined by this method include uranium and sulfur. ![]() Water, acid, and steam are common solvents. In some cases only one hole is used, but the hole has an inner and outer section to separate the in-going solvent from the out-coming solute. This solute or pregnant liquor, as it is often known, is processed to extract the mineral of interest. A solvent is pumped down one hole, and the resulting solution with the dissolved mineral is pumped out another hole. In this method, holes are drilled from the surface into the deposit. Solution mining is used to recover deep deposits that would be uneconomical using underground methods, but only if the ore can be easily dissolved by a solvent. A few examples of commodities mined by this method include sand and gravel. In some cases, the deposits are naturally underwater, while in others the area is flooded, creating an artificial lake on which the dredge operates. This method is used for underwater recovery of loosely consolidated materials using a floating mining machine known as a dredge. A few examples of commodities mined by this method include gold and kaolin. A high-pressure water canon is used to dislodge the deposit, and the resulting solution is either pumped to a processing plant or a gravity separation is performed at the mine site using something like a sluice. Hydraulic mining is used for a limited class of deposits that are characterized as loosely consolidated, such as placer-type deposits. It is sometimes referred to as secondary mining because it is done after the open cast mine has reached an economic limit. This is a method to recover additional coal from under the highwall of a contour mine, when the ultimate stripping ratio has been achieved in open cast operations. Now that I’ve given you the classical mining engineering definition of quarrying, you should be aware that just about everybody uses this word, "quarry" to describe any open pit operation in stone! Oh well… A few examples of commodities mined by this method include Georgia marble and Vermont granite. Unlike open pit mining in which benching is required to prevent failure of the sides or pit slopes, the high strength and competency of the rock mass in quarries is such that vertical walls of 1000’ or more can be excavated. The goal in the mining of these products is to remove large slabs that can be cut and machined to exacting architectural applications. The term dimension stone encompasses certain stone products used for architectural purposes such as granite countertops, marble flooring, and monuments, among a few others. Quarrying is a method of extracting dimension stone. ![]() A few examples of commodities mined by this method include coal and phosphate. One is known as area mining, and is applicable when the terrain is relatively flat and the other is contour mining, better suited for mountains regions. There are two important sub methods for open cast mining. Although it is similar to open pit mining, the distinguishing characteristic is that the overburden is not hauled away to waste dumps but rather, it is immediately cast directly into the adjacent mined-out cut. ![]() Open cast mining is also known as strip mining and is used for bedded deposits, and most commonly for coal. Sutterlin, © Penn State University, is licensed under CC BY-NC-SA 4.0 Open cast mining
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