Supporting any but the smallest lunar facility will require indigenous resources due to the extremely high cost of bringing material from Earth. The Moon has also attracted interest as a resource base to help support near-Earth space activities, because of the potential lower cost once the necessary infrastructure has been amortized. Obviously, initial lunar products will be high-volume, bulk commodities, as they are the only ones for which the economics of lunar production are conceivably attractive. Certain rarer elements, such as the halogens, C, and H, would also be extremely useful (for propellant, life support, and/or reagents), and indeed local sources of such elements would vastly improve the economics of lunar resource extraction. The economic geology of the Moon is discussed

Gillett, Stephen L.

English

NASA Technical Reports Server

LP1 Technical Report 92-06 29
One caution: Detecting radon or polonium from lunar orbit
can reveal the existence and selenographic locations of volatile
reservoirs within the Moon; however, such detections will not
reveal the amount of volatile material within a reservoir, its
composition, how-deeply it is buried, nor how difficult it will be
to gain access to the material. Thus this search technique may
be of more value for the long term, for permanent human set-
tlement of the Moon, than for an initial base.
Proposed Method of Search: It will surprise no one who has
read this far that I am proposing to look for radon and polonium
with an alpha spectrometer from lunar orbit, just as was done
on Apollo 15 and 16. One important difference is that this time
it should be done from lunar polar orbit in order to get a complete
global survey of any significant radon sources.
It would be useful to narrow the selenographic resolution of
detection, if feasible. The maps of2 '°Po distribution produced from
Apollo 15 and 16 data show 2lcPo activity variations for blocks
of the lunar surface 10° wide [11]. It would be very helpful to
be able to locate volatile flows more precisely. By integrating over
several orbits, it should be possible to improve the signal-to-noise
ratio enough to do this [12].
Information of the sort I am proposing may be provided by the
proposed Lunar Prospector mission [12], if and when it flies. That
mission has an alpha spectrometer among its planned suite of
instruments.
References: [1] Bjorkholm P. J. et al. (1973) Proc. LSC 4th,
2793-2802. |2] Gorenstein P. et al. (1973) Proc. LSC 4th, 2803-
2809. [3] Friesen L. j. and Adams J. A. S. (1976) CCA, 40, 375-
380. (4) Middlehurst B. M. (1967) Rev. Geoprryy., 5, 173-189.
[5] Middlehurst B. M. and Moore P. A. (1967) Science, 155, 449-
451. [6] Friesen L J. (1975) Bull. Georgia Acad. Sci., 33, 77.
[71 Smith H. (1990) LP1 seminar. [8] Feldman W. C. (1991) GRL,
18, 2157-2160. [9| Arnold J. R. (1979) JGR, 84, 5659-5668.
[lOlChyba C. F. (1987) Nature, 330, 632-635. [ 1 1 ] Proc. LPSC
4th (1973), Plate V. [ 12] Binder A. (1992) personal communication.
N 9 3 " 17
ECONOMIC GEOLOC)LOGY OF THE MOON: SOME CON-
SIDERATIONS. Stephen L. Gillett, Department of Geology,
Mackay School of Mines, University of Nevada, Reno NV 89557,
USA.
Supporting any but the smallest lunar facility will require indi-
genous resources due to the extremely high cost of bringing
material from Earth [1]. The Moon has also attracted interest
as a resource base to help support near-Earth space activities,
because of the potential lower cost once the necessary infrastruc-
ture has been amortized. Obviously, initial lunar products will be
high-volume, bulk commodities, as they are the only ones for which
the economics of lunar production are conceivably attractive.
Certain rarer elements, such as the halogens, C, and H, would
also be extremely useful (for propellant, life support, and/or rea-
gents), and indeed local sources of such elements would vastly
improve the economics of lunar resource extraction.
However, early scenarios for lunar resources, based on extracting
many common elements from ordinary regolith [2], are probably
unworkable. A survey of terrestrial mining experience indicates
that the overwhelming criterion of a potentially economic deposit
is its recoverable concentration of the desired element [3). This
results because separating elements is difficult and costly, and is
indeed why "ores"—i.e., anomalous concentrations of the desired
element—are worth seeking in the first place. In fact (and some-
what paradoxically), a high-grade ore is most critical for large-
volume commodities, as those would be prohibitive to purify on
the scale required. Hence, identifying the most concentrated
sources of desired element(s) for local resource extraction should
be an element of future lunar missions, and certainly should be
a factor in siting a lunar base.
Few lunar geologic studies to this point, however, are directly
relevant to exploration for potential ores, as they have been
concerned with identifying large-scale, global processes. This focus
has been appropriate, of course, given our a priori ignorance of
the Moon. Moreover, quite apart from the Moon's scientific
interest, serious concern about its resource value would also have
been highly premature, for at least two reasons: (1) Useful con-
straints would be impossible without first knowing the basic geo-
logic framework and (2) potential resources cannot be evaluated
in a vacuum; their value depends on their possible uses. However,
the broad-brush approach of planetological studies is opposite that
of economic geology, because economic geology deals with the
products of rare events. Ore deposits typically occur where by
happenstance a rare process, or a fortuitous combination of pro-
cesses, has run to an extreme. Such deposits are rare by their
very nature; indeed, almost by their very definition. Nonetheless,
they are worth seeking because of the extreme expense of separ-
ating elements, so that it is highly cost effective to let natural
processes carry out as much separation as possible first. Hence,
global characterizations such as typify traditional lunar studies are
not immediately relevant for economic geology investigations.
They merely set the geologic context, whereas economic geology
lies in the unusual—and extremely local—variations from the
norm.
It has been argued, especially in the popular literature, that
the anhydrous nature of lunar materials precludes any ore deposits
like those on the Earth. This is overstated. For one thing, the
Moon is vastly more heterogeneous than had been thought even
until relatively recently, as has been demonstrated by both ongoing
studies of lunar petrology [4] and by remote sensing [5]. The Moon
underwent protracted igneous activity, spanning hundreds of mil-
lions of years, during its early history, and this led to varied and
large-scale differentiation and fractionation.
Second, the mere waterlessness of the lunar environment does
not preclude all ore-forming processes. Although it is true that
water is vital in forming many terrestriql ores, anhydrous magmatic
differentiation is also capable of generating substantial element
concentrations, and indeed has formed some terrestrial ore de-
posits. Such purely magmatic processes include partial melting,
fractional crystallization, and phase separation (liquid unmixing
or crystal settling). Examples of such magmatic ores on Earth
include Cu-Ni sulfide ores from sulfide liquid immiscibility, chrom-
ite from cumulate settling, and magnetite ores crystallized from
late-stage magmatic fluids extremely enriched in Fe [6). Similar
processes may occur on the Moon [7]. Yet other potential lunar
processes may have no terrestrial analogues, as with the possibility
of cold-trapped volatiles in permanently shadowed regions at the
lunar poles [8J.
To be sure, the lunar geologic environment is very different
from the terrestrial, and the possible consequences of the Moon's
low oxidation state and waterlessness for generating useful con-
centrations of elements must be addressed. For-example, consid-
ering the behavior of the rarer elements under lunar conditions
with a view to how (or whether!) they can become concentrated
https://ntrs.nasa.gov/search.jsp?R=19930008060 2020-03-24T07:24:31+00:00Z
30 New Technologies for Lunar Resource Assessment
locally would be valuable. Many industrially important elements
are highly incompatible and in a magma will tend to become
concentrated in the residual melt, so that useful concentrations
may form [7]. However, the enormous literature on lunar rare
elements is focused instead on their use as tracers of large-scale
geologic processes (e.g., partitioning of REE) and thus is not directly
applicable to economic geology.
For example, much lunar Cr is present as Cr", due to the
reduced character of lunar rocks [91, and Cr is enriched in the
lunar crust relative to Earth. The mechanism of this enrichment
seems somewhat obscure, however. Presumably, Cr * is excluded
from compact Fe-Mg silicates in the lunar mantle, as it is a large
ion [10]; moreover, CrT~ has large Jahn-Teller effects and hence
prefers distorted crystal sites. Hence theCron the surface probably
arrived as Cr" in residual melts originally fractionated out of the
mantle. However, surface Cr commonly exists as Cr'~, especially
in chromite [11]. Data from reduced chromian slags indicate that
at low temperatures CrO is unstable and will disproportionate into
Cr metal and CrjO) [12]. As Cr metal is more electropositive
than Fe, this suggests that some of the native Fe on the Moon
may result from reduction by Cr+" oxidation,and textural relations
support this interpretation [13]. In any case, understanding Cr
mobility due to its varying redox behavior may allow finding areas
enriched in it, and may also have implications for deposits of native
Fe.
Moreover, as this example suggests, the slag literature seems
to be a largely overlooked source of possible insights about the
behavior of silicate melts under extremely reducing conditions.
They may provide information on rare elements in particular.
Many slags contain not only Cr++, but Ti4"*"1" or even Ti++
[12]. The ceramic literature may also be useful as many high-
performance ceramics are anhydrous. Indeed, industrial experience
has already provided extremely useful analogues for some non-
terrestrial processes, e.g., Sill's 114] modeling of the role of sulfur
in Venus cloud processes, using observations from Lunge's [15]
industrial treatise on the obsolete lead-chamber process for com-
mercially producing sulfuric acid, and Lee et al.'s [ 16] observations
of molten sulfur flows in commercial mining operations to infer
behavior of natural flows on lo. Such l i terature also seems an
underused source for potential insights into lunar conditions.
Surface Signatures: It is not enough to predict mechanisms
by which ores may be formed; they must also be found. Seeking
a distinctive signature from orbital sensors is an obvious and
relatively cheap approach; e.g., it has been commonly advocated
for detecting whether cold-trapped polar volatiles exist. Many if
not most ore deposits will be too small, however, to show up with
the resolution proposed for probes such as the Lunar Observer.
For example, a deposit of pure ilmenite 100 m on a side, which
would be more than enough to support an initial lunar installation,
would not be seen.
Detection of such small deposits must be more subtle, especially
as global increases in resolution are not practical. Instead, the
signature of potentially favorable geologic settings for concentra-
tion of the desired element must be sought; once such areas have
been identified, they can be targeted for further investigation.
It seems underappreciated that this is how mineral exploration
is carried out on Earth. For example, an explorationist seeking
Au mineralization in Nevada does not begin by mapping the entire
state at 1-m resolution. Instead, he ,or she focuses attention on
promising areas identified on the basis of their general geologic
setting, and maps them in detail. Similarly, small but promising
areas on the Moon, initially found by remote sensing, can be later
focused on in detail with high-resolution sensing, and in the case
of the most favorable areas, actual samples can be collected.
Conclusion: In summary, a viable ore resource contains as
high a concentration of the desired element as possible in a form
that is as easy to recover as possible, and such deposits moreover
are unusual, resulting from rare processes or unusual extremes of
common processes. This will be true of lunar resources as much
as terrestrial ones. To explore for lunar resources, therefore, the
lunar geologic literature must be reevaluated with this perspective,
using our knowledge of global lunar processes to establish geologic
contexts, and then determining what element-concentration pro-
cesses might occur locally in such contexts. Terrestrial analogues,
such as magmatic ore formation, as well as lunar samples that
seem to reflect unusual processes, should help identify such pos-
sibilities. Industrial experience with possibly relevant systems such
as reducing slags or anhydrous ceramics may also provide insight
on possible ore-forming processes. Once possibilities are estab-
lished, then attention can be focused on promising lunar localities.
References: [1] e.g., Lewis J. S. and Lewis R. A. (1987) Space
Resources: Breaking the Bonds of Earth. Columbia Univ. [2] Wal-
dron R. D. and Criswell D. R. (1982) In Space Industrialization,
Vol. II (B. O'Leary, ed.), 1-53, CRC, Boca Raton. [3] Gillett S. L.
(1991) Space Power; Kuck and Gillett, Space Power, submitted.
[4] e.g., Warren P. H. et al. (1983) Proc. LPSC 13th, in JGR, 87,
A615-A630; Warren P. H. et al. (1983) Proc. LPSC 14th, in JGR,
88, B151-B164; Warren P. H. et al. (1986) Proc.. LPSC l f > t h . in
JGR, 90, D319-D330; Vaniman D. et al. (1991) In Lunar Source-
boolc (G. H. Heiken et al., eds.), 5-26, Cambridge Univ. [5] Pieters
C. M. (1986) Rev. Geophys.. 24, 557-578. [6] Guilbert J. M. and
Park C. F. (1986) The Geology of Ore Deposits, Freeman. |7] Haskin
L. A. et al. (1992) In Resources of Near-Earth Space, Univ. of
Arizona, in press. [8] Arnold J. R. (1979) JGR, 84, 5659. [9] e.g.,
Basaltic Volcanism Study Project (1981) Basaltic Volcanism on the
Terrestrial Planets, Pergamon, New York, 1286 pp. [10] e.g.,
Schreiber H. D. and Haskin L. A.(1976) Proc. LSC 7th, 1221-
1259; Basaltic Volcanism Study Project (1981) Basaltic Volcanism
on the Terrestrial Planets, 331, Pergamon, New York; [11] e.g.,
Haskin L. A. and Warren P. H. (1991) In Lunar WcebooJc (G. H.
Heiken et al., eds.), 357-474, Cambridge Univ. [12] Rosenqvist
T. (1983) Principles of Extractive Metallurgy, 2nd edition, 301-302,
McGraw-Hill. 1 1 3] e.g., Reid A. M. et al. (1970) EPSL, 2, 1-5;
Brett R .e t a l . (1971) Proc. LSC 2nd, 301-317. [ 14] Sill G. T. (1983)
fcarus, 53, 10-17. [15] Lunge G. (1903) Sulphuric Acid and Alkali,
Vol. I. 3rd edition, Van Nostrand, New York. [16] Lee S. W. et
al. (1987) LPSCXVIIJ, 545-546.
17250
THE TARGET: H2O ON THE MOON. J. Green 'r,]. Negus-
de Wys2, and A. Zuppero2, 'California State University, CA, USA,
2EG&G Idaho, Inc., ID, USA.
8
The importance of H?O on the lunar surface has long been
identified as a high priority for the existence of a human colony
for mining activities and, more recently, for space fuel. Using the
Earth as an analogue, volcanic activity would suggest the gener-
ation of water during lunar history. Evidence of volcanism is found
not only in present lunar morphology', but in over 400 locations
of lunar transient events catalogued by Middlehurst and Kuiper
in the 1960s. These events consisted of sightings since early history
of vapor emissions and bright spots or flares. Later infrared scan-


Economic Geology of the Moon: Some Considerations

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