seeking out even in remote areas. (Even here, though, technology has been a factor; the deposits targeted by the 1849 California gold rush contained native metal in macroscopic amounts, which could be extracted by extremely primitive means. By contrast, Carlin-type gold in Nevada requires an extremely expensive crushing and extraction technology.) Logistic These are commodities for which transport costs are high, and thus nearby locations have a decided advantage. They are bulk commodities: they have very high volume and low unit cost, so that the tradeoffs of transportation costs versus quality become significant. Little beneficiation or extraction is also required. One example is aggregate for making concrete. For large projects, such as roads or dams, local sources of aggregate are generally found and used. Even then they must be tested and evaluated first. In modern times, no metals on Earth fall into the "logistic" category; it is always cheaper to ship metal rather than mine it locally. There is some historical precedent for local extraction of bulk metal, however, when transportation was still extremely expensive. For example, low-grade siderite (FeCO,) deposits, worked on a small scale by hand, furnished much of America's iron in Colonial times [e.g., Park & MacDiarmid, 1970, p. 407]. They are not now economic because they are far too small and low-grade. It also should be noted that even in ancient times, it was worthwhile bringing rare metal long distances; e.g., Sn from Britain to the eastern Mediterranean. Finally, it should be noted that when logistic deposits are worked, only the high-volume material that requires little processing is extracted; the deposits are not separated into all their constituents. Intermediate cases exist, of course; a porphyry copper deposit that might be economic in Chile, where a mining and transportation infrastructure already exists, and where climatic constraints arc moderate, may not be economic in the Canadian Arctic Archipelago. Nonetheless, for metals the grade and tonnage of a deposit are usually the most important economic considerations. Resources for space development obviously fall into the "logistic" category. At least in the near term, space resources will not be the subject of opportunistic exploitation in the sense of being exported to Earth, except conceivably precious metals from asteroidal nickel-iron [e.g., Kuck, 1979; Lewis & Nozette, 1983]. This immediately implies that (1) near-term space resources will be high-volume commodities; and (2) they should require absolutely minimum processing - i.e., their grade should be as high as possible. Implications for Lunar Resource Development What has all this to do with the Moon? I believe that such constraints as described above will apply to space resources, despite the very high access costs. Such costs also drive the cost of the capital investment - and the maintenance costs! - necessary to extract lunar resources, so to a significant degree the costs are self
RkJQdWJsaXNoZXIy MTU5NjU0Mg==