# Sources of Extraterrestrial Rare Earth Elements: To the Moon and Beyond
## 5 Lunar Resources
### REEs beyond the Moon
Sample NWA 7034 (and two of its paired stones) have been reported by [176; 185; 186] as the first Martian rocks to contain apatite ((Ca\({}_{5}\)(PO\({}_{4}\))(F,Cl));-hosted monazite ((LREE)PO\({}_{4}\)), monazite ((LREE)PO\({}_{4}\))-chevknite-perrierite ((Ce,La,Ca,Th)\({}_{4}\)(Fe\({}^{2+}\),Mg)\({}_{2}\)(Ti,Fe\({}^{3+}\))\({}_{3}\)Si\({}_{4}\)O\({}_{22}\)) in a clast, and coexisting chevkinite-perrierite respectively (Figure 8a). In the most recent study [176], xenotime and merrillite are also reported (Figure 8a). The major mineralogy of these martian surface rocks is characterized by alkali feldspar, plagioclase, pyroxene, with minor magnetite, pyrite, zircon, and phosphates [173; 174; 175] with the newly identified REE-bearing phases listed above all present at the sub-micrometer scale. From [176], monazite was found as inclusions in apatite and was proposed as having an origin associated with fluid-phosphate and fluid-rock interactions occurring at elevated temperatures on Mars, within the source rocks prior to their incorporation into the regolith breccia. These hydrothermal fluids were hypothesized to have originated from igneous intrusions intruding into the martian crust, or from impacts. This latter hypothesis presents a scenario in which REE-mineralization on Mars could be linked to impact cratering and thus presents craters as a potential location for REE- mineral resources on Mars [176]. Beyond samples from the Moon and Mars, other REE-bearing phases within other types of extraterrestrial materials are known. A summary of the REE characteristics of the most common type (broadly classified as stones, or stony-type) is shown in Figure 9.  
Of the 63 bulk rock primitive-mantle normalized REE signatures shown in Figure 9, 61 are chondrites (including samples from the following categories: CI1, CM2, CO3, CV3, EH3, EH4, EH5, EL6, EH6/7, EL7, H4, H6, L4, L5, L6, LL4, LL5, and LL6) and two are achondrites (classification: aubrite). The two aubrite samples represent the two most REE-depleted samples, consistent with their differentiated nature. As has been discussed within the context of lunar and martian samples, REEs are typically concentrated in minor phases. This is also the case with respect to the stony meteorites with sub-mm phosphates (e.g., apatite, whitlockite, and merrillite) and oldhamites ((Ca, Mg, Fe)S) being common carriers of the REEs (up to \(\sim\)1600 ppm, or 0.16 wt. %). These phosphate phases are estimated to constitute \(\sim\)0.6% of the whole rock sample [190] and their REE patterns are shown as insets in Figure 9. Broadly, these REE-bearing phases are enriched by 1-2 orders of magnitude in comparison to the bulk samples but do not extend to the same degree of enrichment as observed in lunar and martian minor phases (Figures 6 and 8). As shown by the bulk stony meteorite data in Figure 9, little difference exists between the different types of chondrites. They exhibit low REE abundances and are therefore unlikely to represent a viable extraterrestrial REE resource. This is consistent with the findings of [191] who discussed the possibility of mining chondritic asteroid materials. While the REEs of these types of extraterrestrial materials are \"not worth mining yet\" and that the mining \"makes little sense\", due to their low abundances, [191] proposed they could be a potential platinum group element (PGE) resource. The PGEs include the  
Figure 9: Summary of the REE characteristics of stony meteorites (chondrites types CI1, CM2, CO3, CV3, EH3, EH4, EH5, EL6, EH6/7, EL7, H4, H6, L4, L5, L6, LL4, LL5, and LL6, achondrite type: aubrite). Data source: [187]). Also shown are two inset graphs which illustrate the REE characteristics of several of the REE-bearing phases found within the stony meteorites. Results from oldhamite are shown in blue (data from from achondrite aubrite samples Bustee and Mayo Belwa, and two EL6 chondrite: Jajh deh Kot Lelu and Khairpur; [188]). Results from apatite and whitlockite are shown in green and purple, respectively (data from H4 chondrite Yamato-74371; [189]).