Optimized multi-microbeam analytical techniques for rapid and accurate identification of lunar minerals: insights from Chang'e-5 basaltic clasts

Abstract

Lunar soils are rare but have great importance for unraveling the evolutionary history of the Moon. The identification of various minerals in lunar soil is vital to explore petrology, geochronology and isotope chemistry of the Moon. However, the rapid and accurate identification of lunar minerals remains technically challenging. Although an automated mineral identification (AMI) method was initially developed to perform mineral identification, the accuracy and analytical conditions of the AMI method are not well-defined. Other microbeam methods, such as electron probe microanalysis (EPMA), Raman spectroscopy (RS) and transmission electron microscopy (TEM), have also been used to identify minerals with various sizes. The applicability of these analytical methods is unclear due to complex mineral phases and diverse grain sizes. In this paper, three Chang'e-5 lunar basaltic clasts were systematically investigated using AMI, EPMA, RS and TEM techniques. Monte Carlo simulation on various minerals was conducted for the first time to optimize the analytical conditions (e.g. accelerating voltage and step size) of the AMI method, which could promote the quick identification of specific lunar minerals. By comparing the minerals identified by AMI, EPMA and RS, the reliability of the AMI method was well validated. Finally, based on the characteristics and applicability of the four methods, an AMI-RS-TEM technical route for identification of lunar minerals was established. This study provides an optimal method for the rapid and accurate identification of lunar minerals, and could also offer valuable insights into mineral identification in other extraterrestrial precious samples (e.g. asteroidal materials and meteorite samples).