than 500 feet from the shaft due to its high maintenance costs. A battery-powered electric rail haulage system was overlaid on the truck and loader system; this necessitated building a different tunnel layout around the shaft station and skip loading pockets. The additional excavation weakened the shaft station pillar, causing cave-ins in the shaft area that required shutting the mine down till repairs could be made. Finally, it should be emphasized that the mining equipment initially installed was not experimental; all of it was standard equipment operating successfully in other mining districts in the United States. Extensive thorough exploration, careful laboratory testing, stepwise pilot-plant testing, and careful plant design will all help to reduce the errors in the design of lunar mine, mill, concentrator and chemical recovery plants. If sufficient flexibility and reserve capacity is designed into the components of a lunar mining, milling, concentrating and chemical recovery system, it might be able to operate at partial capacity until modifications can be made to the system. This might avert a complete shutdown of the plant if the initial configuration did not work as planned. The Earth has innumerable monuments to errors in design and construction of mining and mineral recovery systems. The Moon is all too visible a place on which to build similar monuments to errors and miscalculations. Conclusion Terrestrial mining experience has much to offer in guiding the search for economic sources of space materials. Fundamental lessons from this experience include: (1) the recoverable grade of a potential deposit is its most important economic characteristic, and (2) it is seldom cost-effective to commit to a mine without a great deal of exploration first. Of the mineral deposits found, only a few will be suitable for exploitation. These must be selected on the basis of laboratory and pilot plant testing. Although the Moon is smaller and less complex than the Earth, it is by no means simple, and this complexity affords many opportunities for the existence of exploitable mineral concentrations (ore). The country rock of the few limited landing sites is probably not suitable for exploitation. It will be cost effective to invest heavily in exploration, laboratory testing and pilot plant tests before investment in a lunar mineral exploitation system. REFERENCES [1] Bray, J.L., (1941) Non-Ferrous Production Metallurgy. John Wiley & Sons. [2] Carmichael, I.S.E., E.F. Turner & J. Verhoogen. (1974) Igneous Petrology, McGraw-Hill. [3] Gillett, Stephen E, (1991) "Lunar Resources: Thoughts of an Economic Geologist." Space Power: Resources, Manufacturing and Development, Vol. 10, No. 1, pp. 3-17.
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