Surface mining techniques

The Syncrude operation employs surface mining techniques. Oil sand is removed from the deposit using draglines and placed in windrows where it is reclaimed and transferred to conveyor belts by bucketwheel reclaimers. The oil sand is transported from the mine area, via the 17.7 km of conveyor belts, to the Extraction facility. 

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. 

Surface mining techniques are used when the coal is present near the surface, and the overburden is thin enough. These techniques include contour mining, strip mining, and auger mining. 

Fig. 3. Early method of contour surface mining. This was the predominant way of mining throughout Appalachia until passage of stringent legislation that ushered in a new integrated mining technique. [Caterpillar Ini)...

Auger mining is a supplementary method used to reach coal in stripped areas where the overburden has become too thick to be removed economically. Large augers are operated from the floor of the surface mine and bore horizontally into the coal face to produce some reserves not otherwise minable. This technique is frequently used to supplement coal recovery from contour mining. 

Smface minir is less expensive and safer than tm-dergromrd mining. About 90% of the rock and mineral resources mined in the United States and more than 60% of the nation s coal is produced by surface minir techniques. Coal mining accomrts for abotrt half of all sitr-face mining, extraction of sand, gravel, stone, and clay for another 35%, phosphate rock for about 5%, and all metallic ores, for abotrt 13%. 

By the evaporation of large inland seas or land-locked lakes of large drainage basins in geologic history, extensive subterranean deposits of sodium chloride and other salts in layers of cumulative thickness as great as 400 m have been laid down in many parts of the world. Deposits in well-consolidated strata and less than 500-600 m below the surface are usually economic to work by conventional mining techniques. In Canada, these accessible deposits amount to about 74% of the total and in the U.S.A., about 35% of the total [1, 2]. 

The surface exposures and the near surface deposits (<45 m of cover) of the Athabasca region can be strip-mined for bitumen recovery. They amount to about 10% of the Athabasca deposit. The remainder of the Alberta tar sands lie under 75 m or more of overburden. It is uneconomical to surface mine, and too poorly consolidated for underground mining. These deeper deposits are yielding bitumen to the surface via various in situ techniques. 

Other tests, such as the respirator qualitative/quantitative fit test method, refer to a Bureau of Mines technique of blowing a stream of talcum powder or coal du.st directly around the face to facepiece seal. The user then would remove the respirator and the leakage would be revealed by telltale streaks of the dust or powder. This method is rarely used. Uranine (a fluorescein dye) can also be sprayed around the respirator sealing surface and, when removed, the leaka was detected by a fluorescent light source. 

Underground mining techniques are somewhat more labor-intensive than surface mining and are used to remove coal located below too much overburden for surface mining but here, too, machines are used in most instances to dig, load, and haul the coal. Access to the coal seam is through a drift (horizontal passage), a slope, or a shaft (Fig. 17.6), depending on the location of the coal seam. 

Diverse techniques have been employed to identify the sources of elements in atmospheric dust (and surface dust) (Table V). Some involve considering trends in concentration and others use various statistical methods. The degree of sophistication and detail obtained from the analyses increases from top left to bottom right of the Table. The sources identified as contributing the elements in rural and urban atmospheric dusts are detailed in Table VI. The principal sources are crustal material, soil, coal and oil combustion emissions, incinerated refuse emissions, motor vehicle emissions, marine spray, cement and concrete weathering, mining and metal working emissions. Many elements occur in more than one source, and they are classified in the... 

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