then be obtained for laboratory testing. Asteroidal materials, another commonly proposed source for extraterrestrial resources, are even less well characterized. Although the compositions of certain meteorites recovered on Earth are encouraging for possible resource value, ambiguities remain in the relation of meteoritic and asteroid compositions (e.g., Lipschuk et al., 1989). More importantly, we still have no idea of the in-situ heterogeneity of the meteorite parent bodies, including their degree of fracturing or consolidation, the lateral continuity of rock types, the grain size distribution, the presence and/or degree of alteration and vein filling, and most critically, the distribution of the desired element(s) with respect to these small-scale textures. This is the sort of information, as emphasized elsewhere in this paper, that is critical to reasonable extraction scenarios. Much further exploration is required before asteroids can be considered seriously for resource extraction. As for the Moon, some of this exploration can be done remotely, by space-probe missions, to map and sample in-situ material at small scales, and will be needed before any processing scenarios can be constructed. Laboratory Testing Initial laboratory tests will be on samples collected during exploration. The laboratory location may be on the lunar surface, in orbit or on Earth. Although an orbital location may be the most convenient since numerous samples from a large number of locationswill probably need to be tested on an ongoing basis, many tests will require gravity, and simulating gravity on the scale required may be too expensive. These tests may include assaying, crushing, grinding, trying various mineral separation methods; grading of various mineral concentrates, middlings, and tailings; and recovery testing. The goal will be to maximize concentrate grade yet still recover a significant percentage of the ore mineral from the ore. In order to make a sufficiency high-grade mineral concentrate, however, total recovery may be less than 50%. High grade alone, moreover, may not be enough to make a particular rock an ore, because of inability to make a high-grade mineral concentrate from it. In early 1965, for example, Kennecott’s Ray, Arizona open-pit copper mine had to abandon a million-ton block of ore-grade sulfide mineralization because the chalcocite (CuS) was so fine-grained that grinding could not liberate it from the silicate gangue. Hence, flotation would not work for concentration. Similarly, it was mentioned above that extremely fine-grained, Carlin-type gold cannot be recovered by density separations; cyanide leaching must be used, and in some cases the leaching does not work because of cyanide scavenging by other minerals in the rock. Once a mineral concentrate is made, chemical separation tests can be made to determine the quality and recovery of the desired element or elements. Even a high-grade concentrate may be unusable if it contains too many of the wrong impurities, such that undesirable side reactions occur during chemical processing. For example, some lunar ilmenites contain micron-sized grains of troilite (FeS).
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