Lunar Resources: Thoughts of an Economic Geologist STEPHEN L. GILLETT SUMMARY From terrestrial experience, the most important characteristics of a potential ore deposit are its grade and tonnage; i.e., the degree of concentration of the desired material, and the total amount of the material. Despite - even because of - the high cost of access to space, these characteristics are likely to be extremely important for space-derived resources as well, because such resources, at least in the near term, will be high volume commodities. Hence, it will probably be cost-effective to do a great deal of additional investigation of the Moon before committing to a specific, large-scale mining process. Local concentrations of common lunar elements are highly probable, and even anomalous concentrations of rare elements cannot be ruled out. Introduction It has long been noted that because of the high cost of access to space from Earth, other sources of raw materialswill be necessary for construction of extensive space facilities [e.g., Lewis & Lewis, 1987], The Moon is an obvious source of extraterrestrial raw materials: it is always nearby, it has a shallow gravity well, it is airless, and its geologic framework is already roughly known. Much speculation about lunar resources, however, appears to lack the perspective developed from centuries of exploring for resources on Earth. For example, the observation that average lunar regolith is about 75% "demandite" [Waldron & Criswell, 1982] is merely equivalent to stating that the Moon is made of common rocks. Such rocks are not mined on the Earth for their elements; the economics of such a separation would be horrendous, and this will almost certainly be true on the Moon as well. Indeed, terrestrial ore materials are not split into all their constituents; to be sure, some by-products are recovered, but even so the cost of extracting all elements remains prohibitive. Such other elements are more cheaply won from their own ores. The concept of obtaining all resources from common rocks also overlooks the value of a planet-sized body as a resource base. The welter of natural processes on a planet-sized body ensures that in rare cases a fortuitous combinations of circumstances will have caused anomalous concentrations of valuable elements that can be exploited - and as will be seen, the concentration of a desired material is one of the most vital parameters in determining whether a deposit is economic. To be sure, the Moon does not have the vast array of on-going geologic processes that the Earth does, in particular those in which water is involved. Nonetheless, the Moon is a good deal more complicated than is generally recognized in the non-specialist MacKay School of Mines, University of Nevada, Reno.
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