of sinking an exploration shaft to explore the mineralized zone, they did not find that it could not be mined until after they had spent a fortune on a useless mine, mill and concentrator. The western United States has numerous such monuments to trying to save money by skipping mine development steps. Full Scale Mine Concentrator and Recovery Plant Start Up After rejection of the vast majority of deposits found in the exploration stage, due to their failing the laboratory and pilot plant testing, one or more deposits are selected for development. In spite of all the care taken up to this point, most plants initially fail to operate as designed. Many can be improved and made to operate satisfactorily by subsequent modification. Although mistakes will be made, these mistakes hopefully can be corrected at a reasonable cost without destroying the operation. For example, at the startup of the Copper Cities mine near Miami, Arizona, the water did not separate properly from the tailings; the thickener overflow carried suspended solids that would destroy the clear-water pump seals and erode the impellers. The fact that the upper part of the ore had excessive non-settling clays ("slimes") had been observed in the early laboratory tests but was later overlooked. Thus, a hydroseparator and flocculent feeding equipment were added to the tailings processing stream to save the pumps. The suspended clays also threatened the tailings dams, since the slimes did not separate from the sands at the dam face to form a clean sand dam behind which the slime tailings would be retained. "Cyclones" (centrifugal separators) had to be purchased and installed on the tailings dam to separate the sands from the slimes. In this case, these expensive retrofits worked. Other examples come from the many horror stories stemming from the over-hasty development of the Ambrosia Lake uranium district in New Mexico during the uranium rush of the late 1950s. In the hurry to get mines and mills into production, the ability of the mining, milling and recovery equipment to operate under conditions in the district was not investigated so that nearly disastrous mistakes compelled major equipment redesign, redevelopment and retrofitting. Fortunately the companies involved had the financial resources to withstand this huge financial drain. However, all the costs were not monetary: in one fiscal year there were sixteen separate fatal accidents plus many serious injuries. Disastrous choices of equipment were made. A whole fleet of brand new D-6 Caterpillar front-end loaders had to replaced, after only six months’ use, with new articulated rubber-tired front-end loaders. Electric loaders and blast hole drills had to be scrapped after a few weeks’ use because the electrical systems could not be maintained under the wet conditions in the mines. Electrical connectors exploded when acidic mine water, an electrolyte, seeped in past the seals. The electric-powered loaders and drills were replaced with air-powered equipment, which required purchase, design, and construction of a large compressed-air system for the mines. Moreover, the rubber-tired equipment was found to be unusable more
RkJQdWJsaXNoZXIy MTU5NjU0Mg==