Ti distribution in grain-size fractions of Apollo soils 10084 and 71501

Much work has been devoted to the correlation between the remotely sensed UV-VIS slope and the TiO2 concentration of the lunar surface, and this correlation has been used to map the lunar surface TiO2 distributions using data obtained from various missions. However, additional work is needed to fully evaluate the UV-VIS-TiO2 correlation. Such work would help ongoing efforts to improve TiO2 mapping (e.g., as currently underway with LROC Wide Angle Camera (WAC) data). To evaluate the UV-VIS-TiO2 correlation, we are investigating soil petrographic factors (e.g., modal abundances of Ti bearing minerals, lithic, and glass hosts, ilmenite morphology, grain size, and maturity) that may influence the spectra. This “ground truth” approach will be useful in comparing between sample information and laboratory spectra to investigate the influence of petrographic factors on the spectra. In this work, we report the quantitative results of a systematic laboratory investigation of three size fractions (210-100 μm, 100-48 μm, 48-20 μm) of two high Ti lunar soils 10084 and 71501 using a combined digital imaging (backscattered electron image and X-ray maps) method. For each size fraction, the results include: (1) the modal abundances for single phase minerals and lithologic components; (2) the Ti distributions among Ti host components; and (3) the shape of ilmenite grains. We compile and compare the data together for the three size fractions of the two high Ti soils with different maturities as well as data from previous studies. Future work will include the investigation of finer size fractions (<20 μm) and more samples (Apollo 12, Apollo 15) covering a larger range of Ti concentration and maturity, and comparison with their spectra.