Wittenberg, Santarius, and Kulcinski (1986) further calculated that, even if the U.S. electrical demand doubled every 25 years until the 22nd century and deuterium/helium-3 fusion provided all the electrical energy required after the year 2020, on!y 3 percent of the Moon's 3He resources would be used. In addition, they concluded that" It should also be possible to use the lunar surface as a source of fuel for power plants in earth orbit, on the moon or on other planets. This lunar source of 3He is sufficiently large to provide for a century or more of space research to exploit the extremely large 3He reserves on Jupiter. Thus, the lunar 3He can help deliver the 'clean' energy source that fusion scientists have been promising for over 30 years."
Fumaroles and Vapor Deposits
As I have stated previously, there is little direct evidence that fumaroles exist or ever existed on the lunar surface. The observation of gaseous emanations from the crater Alphonsus by Kozyrev (1962) and the probable fire-fountaining origin of the orange glass spheres (McKay and Heiken 1973) suggest that volcanic gases occur on the Moon. The crystallization of subsurface magma should release dissolved volatiles and, if these volatiles accumulate, then fumarolic activity should occur (Sato 1979), with possible deposition of volatile species. Another source of volatiles is emanations from the lunar interior (Gorenstein, Golub, and Bjorkholm 1974; Hodges and Hoffman 1974; Geake and Mills 1977; Middlehurst 1977; Runcorn 1977). Fumarolic- like activity may also occur through the remobilization Qf material from the heating associated with major meteoritic or cometary impacts (McKay et al. 1\972, Jovanovic and Reed 1975, Cirlin and Housley 1980). The discovery by McKay et al. (19.72) of vapor-deposited apatite, ilmenite, metallic iron, plagioclase, pyroxene, and troilite in recrystallized Apollo 14 breccias is an example of remobilization of elements by a major impact event.
The permanently dark and cold areas of the lunar polar regions may be a source of cryotrapped volatiles (Watson, Murray, and Brown 1961; Arnold 1979; Lanzerotti, Brown, and Johnson 1981). Temperatures possibly as low as 40 K suggest the possibility of both surface and subsurface ices that could survive for billions of years. However, until exploration of the polar regions occurs, we can only speculate as to the possible presence and nature of ices (Staehle 1983). If they occur in useful quantities, they will provide an overwhelming reason for locating at least some part of a base complex near a pole (Burke 1985).
Nonlunar Materials
There are two basic types of nonlunar inputs: (1) meteoritic, including cometary, and (2) solar wind. The rocks from which the lunar regolith is formed are fragmented by meteoritic and cometary impacts. This process results in the input of material of nonlunar sources (Ganapathy et al. 1970, Baedecker, Chou, and Wasson 1972; look 1975). The fragmented material, with its included nonlunar material, is a potential resource. For example, if large masses or concentratable fragments of chondritic materials can be located, they will be a source of volatile elements (Taylor 1975). Meteoritic debris is also a source of metallic iron, nickel, and cobalt (Dalton and Hohmann 1972; Goldstein and Axon 1973; Goldstein, Hewins, and Axon 1974; Wanke, Dreibus, and Palme 1978; Mehta and Goldstein 1980) and a potential source of the platinum group elements and gold (Ganapathy et al. 1970, Wlotzka et al. 1972, Hertogen et al. 1977).
Discussion
The surface of the Earth is dominated by water-related erosional processes, oxidation, and biological activity, whereas the surface of the Moon is dominated by bombardment processes (table 1). Internal crustal processes for both the Earth and the Moon are dominated by metamorphic reactions in which water plays an important role on Earth (figs. 3 and 4). There is no evidence of free water on the Moon. The lack of free water on the Moon significantly affects the nature of possible ore deposits on the Moon and eliminates the classes of ore deposits that are most exploitable on Earth; namely, (a) hydrothermal, which includes all base metal sulfide and precious metal vein deposits; (b) secondary mobilization and enrichment, which includes all ground-water-related ore deposits; (c) direct precipitation from a body of water, which includes evaporite deposits such as gypsum and salt; and (d) placer, which includes heavy mineral deposits such as diamond, gold, ilmenite, monazite, rutile, and zircon. These types of ore deposits have made up a significant percentage of the ores mined on Earth, because these processes concentrate the elements and the heavy minerals into exploitable deposits.
The data in tables 1 and 2 and the evaluation of figures 3 and 4 offer no evidence, direct or theoretical, for significant base metal sulfide or precious metal vein deposits on the Moon. However, we must be somewhat cautious about making categorical statements, because only nine lunar landing sites (six manned Apollo and three unmanned Luna) have been sampled and these were not chosen at random. Even though meteoritic processes result in throw-out of materials and thus a potentially wide distribution of fragmented rock types, there could be small, localized, but very concentrated sources of desirable elements or compounds that would go unrecognized in studies of particles among the returned lunar regolith fines. If concentrations of desirable elements or compounds do occur, they should be found in igneous rocks, meteoritic and cometary debris, and regolith fines that have been affected by solar wind implantation (table 2; figure 3).
In 1985 I made a pioneering effort to evaluate quantitatively the lunar regolith fines as a primary source of hydrogen. The theoretical foundation laid in that paper can be used to evaluate quantitatively any solar-wind-implanted species or any species found on or near the surface of a particle, no matter what its origin.
The known concentration range of hydrogen, nitrogen, and carbon in the lunar regolith fines is shown in table 10. Such values are often used as evidence that the Moon is devoid of water, even though 100 ppm of hydrogen is equivalent to 0.09 percent by weight of water. In addition to water, other elements necessary for the growth of plants-nitrogen and carbon (carbon dioxide)-are also present on the Moon. However, because these three elements together total less than 0.3 percent of the lunar regolith (table 10), they must be beneficiated (concentrated) before they can be economically extracted. Beneficiation of lunar regolith fines can only occur under the following conditions: (1) A relatively small portion of the fine material must contain a significant amount of the element sought. (2) That material must be separable; that is, it must have unique physical and chemical properties. (3) The separation process must be economical; that is, not labor intensive or technically complex.
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