Chemical analysis of terrestrial Mn-enriched samples

Chemical analyses of terrestrial Mn-enriched samples supporting the manuscript "Elucidating the mineralogy of terrestrial sedimentary manganese minerals using trace elements with relevance for Gale crater, Mars" to be submitted to the Journal of Geophysical Research: Planets. X-ray Diffraction (XRD) for mineralogy To determine the mineralogy of Mn minerals, samples were powdered by mortar and pestle and analyzed by powder XRD at University of New Mexico using a Rigaku SmartLab diffractometer. Samples were mounted as randomly oriented powders, and diffraction patterns were collected with a beam size that was substantially larger than the analyzed grain size. The samples were scanned from 5 to 70°2θ using Cu Kα radiation (1.5406 Å) operated at 45 kV and 40 mA at steps of 0.008° and a scan rate of 1.63° min-1. Diffraction patterns were compared with the International Centre for Diffraction Data (ICDD) database using Rigaku PDXL software. Inductively coupled plasma mass spectrometry (ICP-MS) for trace elements Terrestrial samples were powdered by mortar and pestle and submitted to Activation Laboratories Ltd. (Actlabs, Canada) for ICP-MS to determine elemental abundances. Hydrochloric, nitric, perchloric, and hydrofluoric acids were used for digestions of samples. This total digestion allows for quantification of most minor and some major elements except for Ta, Nb, As, Sb, Sn, Hg, Cr, Au, and U. The lab’s detection limit is taken as analytical precision. Laser Induced Breakdown Spectroscopy (LIBS) for elements Terrestrial samples were analyzed by LIBS using the ChemCam engineering model at Los Alamos National Laboratory in Los Alamos, New Mexico. All samples were analyzed under 7 torr CO2 to simulate martian conditions and at a standoff distance of 1.6 m to simulate data collection from the rover. Samples CB_14, CY_25, and CB_38 were analyzed as cut core surfaces. Samples LW_Mass, LV_FM, and LW_Nod were analyzed as whole rocks with natural rock surfaces, and samples POX6, PAN1, MO5, and O99 were powdered and pressed into pellets for analysis. Each sample was shot in 5 locations with 30 shots for each location, like a typical ChemCam LIBS analysis on Mars. The LIBS data were processed following the same method as Mars data received from ChemCam LIBS on Curiosity. The first 5 analysis shots at each location for each sample were omitted to maintain consistency with data acquired on Mars; the first ~5 shots typically contain a contribution from surface dust and are thus removed to better represent the composition of the rock. Major elements Si, Ti, Al, Fe, Mg, Ca, Na, and K were quantified based on the shot-averaged LIBS spectra using the methods of quantification employed for Mars LIBS data: partial least squares (PLS) and independent component analysis (ICA), multivariate techniques.