Mineral Resources by Manuel Bustillo Revuelta
Author:Manuel Bustillo Revuelta
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham
Where choosing between surface and underground methods, there are many factors, both quantitative and qualitative, that must be evaluated to select the mining method. Some of the factors that must be considered include (a) size, shape, and depth of the deposit; (b) geological structure and geotechnical conditions; (c) productivities and machinery capacities; (d) availability of experienced work force; (e) capital requirements and operating costs; (f) ore recoveries and revenues; (g) safety and injuries; (h) environmental impacts, during and after the mining; (i) reclamation and restoration requirements and costs; and (j) societal and cultural expectations (Nelson 2011). For example, if the mineral deposit lies horizontal, it is commonly mined through either surface or underground mining methods, but not both; instead, for a steeply dipping vein or massive deposit that outcrops on the surface and extend very deep, the best strategy is often to mine at first using surface methods and then changing to underground mining. In fact, the ore-to-waste ratio is the principal feature in the choice between surface and underground mining.
Although both methods have benefits and drawbacks, surface mining is usually a more profitable method than underground mining. In terms of daily production tonnage, surface mines are almost always larger than underground mines producing the same commodity. This is because surface mines must extract much higher waste rock, whereas many of the underground mines extract the same mineral more selectively and with less dilution. With all other conditions equal, surface mining is normally regarded as preferable, because of lower development costs, quicker start-up time, and lower number of accidents; the underground mining environment is recognized as being more hazardous than the surface environment. Underground mining is generally more expensive than surface mining since it is more capital intensive. Surface mining is also preferred because it does not need to extract an excessive amount of waste rock to access the ore.
In an underground mine, a significant amount of infrastructure must be installed before mining begins, in which that large capital investment is often necessary before production can start. The development of a large underground mine can take as many as 5–10 years. Interest costs during this time will therefore be high and can comprise 30–40% of the pre-mining capital requirements before mining can start. However, for large tonnage production, capital and operating costs are commonly higher for surface mines. In these cases, a dual feasibility study must be performed comparing the surface option to the best underground mining option. In all circumstances, capital costs increase and operating costs decrease with increasing production tonnage.
The time between overburden removal and the mining of the product mineral in surface mines should be as short as possible to optimize overall cash flow. Otherwise, high preproduction development costs are produced, and the interest costs during development are high and represent a significant portion of the pre-mining capital requirement before mining can start (Nelson 2011). The dominance of surface operations (ICMM 2012) (◘ Fig. 5.4) is based on the amount of rock handled, many times mainly the removal of overburden, which is often drilled and blasted.
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