Apatite Chemistry as a Promising Tool for Targeting Lunar Resources

APATITE CHEMISTRY AS A PROMISING TOOL FOR TARGETING LUNAR RESOURCES. G. Consuma1, F. McDonald1, and J. Carpenter1. 1 European Space Agency, ESTEC, Keperlaan-1, 2201 AZ Noordwijk, The Netherlands ([email protected]) Introduction: The Moon’s potential as a resource-rich environment for space exploration and sustained human presence has gained increasing attention in recent years. Understanding and utilizing lunar resources is becoming essential for supporting long-term space missions and reducing dependence on Earth for critical materials. However, several key aspects of lunar resource exploration, particularly the spatial distribution and concentration of economically viable ore deposits within the lunar crust, as well as effective resources targeting methodologies remain inadequately defined [1]. This preliminary study introduces a novel approach to lunar resources targeting by applying mineral chemistry tools, approaches that have been proven successful in terrestrial mineral exploration but have yet to be adapted and tested for lunar applications. By leveraging available in-situ chemical analyses from returned samples, we propose a mineral system framework to better understanding the geological processes underlying the presence of lunar resources. Additionally, this framework outlines key chemical proxies that could be instrumental in identifying such resources. Apatite as an exploration tool: learnings from Earth Apatite (Ca₅(PO₄)₃(F, Cl, OH)) is a phosphate mineral known for its ability to host significant quantities of volatile elements such as chlorine, fluorine, and hydroxyl (a water proxy), along with rare earth elements (REE). For terrestrial mineral exploration purposes, apatite is widely used as key indicator of ore deposits [2,3], including iron oxide – apatite (IOA), iron-oxide-copper-gold (IOCG); nichelcopper sulfide deposits, porphyry copper deposits, as well as mafic layered intrusions. The chemical composition of apatite can, in fact, provide valuable proxies for distinguishing mineralized from unmineralized regions. For instance, apatite from mineralized areas typically contains higher calcium content and lower concentrations of trace elements that partition into the calcium sites (e.g., REE, Y, Mn, Sr, Pb, Th, and U) compared to apatite from unmineralized rocks [2]. Chemical ratios such as Ce/Tb and Eu/Eu* also serve as useful proxies for identifying mineralized regions. These approaches are effective not only in magmatic and hydrothermal systems but also when using detrital apatite chemistry to uncover buried mineral deposits in glaciated terranes. Additionally, the ability of apatite to sequester volatiles like chlorine and sulfur aids in understanding metal mobility, as these elements promote the transport of metals as complexes from the magmatic source to ore deposition sites. Recent scientific efforts have increasingly focused on utilizing the volatile chemical signatures of apatite as a proxy for metal concentrations within the Earth’s crust, demonstrating their potential in ore exploration [4,5,6]. Apatite inclusions in zircon are particularly valuable, as they preserve the original magmatic volatile signature, unlike groundmass apatite, where volatiles are very likely degassed or diffused [7]. The textural occurrence of apatite is therefore also crucial for capturing an intact magmatic volatile history. Lunar apatite for targeting resources on the Moon Apatite is a widespread accessory mineral in lunar rocks, present in both volcanic basalts and highlands' crustal rocks. Despite extensive research has focused on apatite’s role in tracing the lunar volatile history, its potential connection to metal concentrations is unexplored. Studies have shown the volatile content of apatite across various lunar rock types, including KREEP, very high potassium (VHK), low-Ti and high-Ti basalts, as well as high-Ti and high-K mare basalts, and rocks from lunar highlands [9]. While these studies reveal significant heterogeneities in volatiles composition, more detailed and targeted approaches are needed to understand the metallogenic potential behind these chemical signatures. For example, variations in sulfur and chlorine isotopic composition of apatite among Apollo samples indicate substantial heterogeneity, but a narrow range of heavy δ37Cl values of apatite in KREEP basalts may suggest a link between chlorine degassing (loss of light chlorine isotope) and REE-enriched regions [10]. Additionally, studies have highlighted differences in volatile content in apatite based on textural occurrences, similar to terrestrial apatite. Notably, higher OH content (ca. 780 ppm H2O) has been measured in early-crystallized apatite inclusions in pyroxene from KREEP basalt 1538, compared to apatite grains associated with late-stage mesostasis areas. These findings emphasize the importance of studying mineral inclusions for assessing magmatic volatile sources and their potential connection to metal mobility [8]. To address these complexities and account for the differences in geological processes between Earth and the Moon, we therefore discuss the application and adaptation of terrestrial mineral exploration strategies to lunar geology. This mineral approach aims to provide the foundation for future analytical strategies, improve exploration methods by making them more efficient and targeted, and ultimately contribute to the development of a sustainable framework for lunar resource utilization. References: [1] Crawford I. A. (2015) Progress in Physical Geography, 39, 137–167. [2] Mao M. et al. (2016) Economic Geology 111, 1187–1222. [3] Qiu, K. F. et al. (2024) American Mineralogist 109, 303–314. [4] Consuma, G. et al. (2024) EGU General Assembly, 19743. [5] Huang M. L. et al. (2023) Economic Geology, 118, 5, 1201-1217. [6] Lormand C. et al. (2024) Lithos 480–481, 107623. [7] Kendall-Langley L. A. et al. (2021) Contrib Mineral Petrol 176, 58. [8]. Tartèse, R., et al. (2014) Geology 42, 363–366. [9] McCubbin, F.M. et al. (2015) American Mineralogist 100, 1668–1707. [10] Faircloth S. J. (2020) PhD Thesis, the Open University.