Underground mining

A carefully planned network of shafts, drifts, and raises are the requisites of a producing underground mine. The word development stands for the preparation of this network. In normal development one can recognize four different kinds of rock excavation and they are shafts, drifts, raises and inclines. The main aim of provision of a shaft is to provide access to or a connection with underground. This access may be utilized for a variety of purposes hoisting rock and ore, personnel and material transport, ventilation, etc. Most modem shafts 

The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and the geology and environmental factors. Coal-mining processes are differentiated by whether they operate on the surface or underground. Many coals extracted from both surface and underground mines require washing in a coal preparation plant. 

Typically, seams relatively close to the surface, at depths less than approximately 200 ft, are usually surface-mined. Coal that occurs at depths of 200-300 ft is usually deep-mined but, in some cases, surface-mining techniques can be used. For example, some coals in the western United States occur at depths in excess of 200 ft are mined by open pit methods—the thickness of the seam (60-90 ft) renders the method economically feasible. Coal deposits occurring below 300 ft are usually deep-mined. 

To reach deeper coal beds, miners typically dig underground mines. Two or more shafts are tunneled down into a coal seam—typically, different shafts are used for the passage of miners and machinery and for the passage of mined coal. 

There are three types of underground mines (1) shaft mine, (2) slope mine, and (3) drift mine. The type excavated in a particular case depends on the depth of the coal deposit, the angle of the coal bed, and the thickness of the coal seam (Lindberg and Provorse, 1977 Euler, 1981). 

On occasion, any one mine may have all three types of openings (i.e., drift, slope, and shaft). 

---

Mining. Underground mining procedures are used for deep fluorspar deposits, and open-pit mines are used for shallow deposits or where conditions do not support underground mining techniques (see Mineral RECOVERY AND PROCESSING). 

Limestone Production. Because more than 99% of U.S. limestone is sold or used as cmshed and broken stone, rather than dimension-stone, most of the description of limestone s extraction and processing herein focuses on the former (Fig. 4). Most stone is obtained by open-pit quarrying methods. Underground mining is pursued by some important operations, but the toimage quarried exceeds that mined by nearly 20-fold. There is, however, a slight trend toward increased mining which should continue. 

Mining of the ore deposit constitutes a significant cost, especially in hard rock mining. Mining costs vary considerably from ore to ore and from a few cents to well over 100/t mined. Underground mining is the most expensive hydrauHc mining of sedimentary deposits is the least expensive. 

Open-pit zinc mining is not common, since most mines ate below the surface. The Kidd Creek Mine in Ontario, Canada, is a combination open-pit—underground mine. It is one of the richest deposits in the world with an estimated 62.5 x 10 t grading 7.08% zinc, 1.33% copper, and 151 g silver (14). Underground mining methods include room-and-pdlar, shrinkage, cut-and-fill, and square set. In the United States, ca 20 mines account for more than 98% of zinc production. 

The commercial value of a clay deposit depends on market trends, competitive materials, transportation faciflties, new machinery and processes, and labor and fuel costs. Naturally exposed outcrops, geological area and stmcture maps, aerial photographs, hand and power auger drills, core drills, earth resistivity, and shallow seismic methods are used ia exploration for clays (32). Clays are mined primarily by open-pit operation, including hydraulic extraction however, underground mining is also practiced. 

The mechanical equipment used in room-and-pikar underground mining usuaky involves a series of specific operations with continuous mining equipment. Continuous miners use rotating heads equipped with bits to pick or cut through the coal without blasting and load it into a shuttle car for conveying to a belt system. 

The weighted average values fob underground and surface mines decreased from 28.24/1 iu 1984 to 23.99/t iu 1990 (2). Underground mine prices decreased from 36.66/t to 31.51/t, whereas surface mine prices dropped from 22.70/t to 18.72/t. 

In 1955 it was discovered that mixtures of ammonium nitrate and fine coal dust have satisfactory blasting capabilities in large (9 inch) holes used in open-pit coal mines to remove the rock and soil covering the coal. Polyethylene bags containing this material deform to fit the hole and provide moderate water resistance. ANFO is used in open-pit iron and copper mines and for construction such as road building. The mixture is air blown into 2-inch holes or less m maiiv underground mines. 

Talc, unlike Che micas, consists of electrically neutral layers without the interleaving cations. It is valued for its softness, smoothrtess and dry lubricating properties, and for its whitertess, chermcal inertness and foliated structure. Its most important abdications are in ceramics, insecticides, paints and paper manufacture. The more familiar use in cosmetics and toilet preparations accounts for only 3% of world production which is about 5 Mt per annum. Half of this comes from Japan and the USA. and other major producers are Korea, the former Soviet Union, France and China. Talc and its more massive mineral form soapstone or steatite arc widely distributed throughout the world and many countries produce it for domestic consumption either by open-cast or underground mining. 

The use of underground mining methods requires integration of transportation, ventilation, ground control, and mining methods to form a system that provides the highest possible degree of safety, the lowest cost per ton of product, the most suitable quality of final product, the maximum possible recovery of coal, and the minimum disturbance of... 

Coal from underground mines is assessed an excise tax of 1.10 per ton, and coal from surface mines is assessed a tax of 0.55 per ton, but in each case, a constraint is added that states that the tax cannot exceed 4.4 percent of the sales price. The receipts from these taxes are allocated to the Black Lung Disability Trust Fund. Monies from this trust fund are used to pay for health benefits to coal miners. 

FPN) Group I electric apparatus is intended for use in underground mines. See Section 90-2(b) (2). 

The Break Even Stripping Ratio (BESR) or the economic limit for surface operations in comparison with underground mining is therefore determined as ... 

Underground mining/cost tonne ore-surface mining cost/ton ore... 

O. Hamrin, Choosing an Underground Mining Method, In Underground Mining Methods Handbook,... 

---