Sulfide ores are a major source of noble (Au, Ag, and Pt) and base (Cu, Pb, Zn, Sn, Co, Ni, etc.) metals and will, therefore, be vital for the self-sustainment of future Mars colonies. Martian meteorites are rich in sulfides, which is reflected in recent findings for surface Martian rocks analyzed by the Spirit and Curiosity rovers. However, the only high-resolution (18 m/pixel) infrared (IR) spectrometer orbiting Mars, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), onboard the Mars Reconnaissance Orbiter (MRO), is not well-suited for detecting sulfides on the Martian surface. Spectral interference with silicates impedes sulfide detection in the 0.4–3.9 μm CRISM range. In contrast, at least three common hydrothermal sulfides on Earth and Mars (pyrite, chalcopyrite, marcasite) have prominent absorption peaks in a narrow far-IR (FIR) wavelength range of 23–28 μm. Identifying the global distribution and chemical composition of sulfide ore deposits would help in choosing useful targets for future Mars exploration missions. Therefore, we have designed a new instrument suitable for measuring sulfides in the FIR range called the Martian far-IR Ore Spectrometer (MIRORES). MIRORES will measure radiation in six narrow bands (~0.3 µm in width), including three bands centered on the sulfide absorption bands (23.2, 24.3 and 27.6 µm), two reference bands (21.5 and 26.1) and one band for clinopyroxene interference (29.0 µm). Focusing on sulfides only will make it possible to adapt the instrument size (32 × 32 × 42 cm) and mass (<10 kg) to common microsatellite requirements. The biggest challenges related to this design are: (1) the small field of view conditioned by the high resolution required for such a study (<20 m/pixel), which, in limited space, can only be achieved by the use of the Cassegrain optical system; and (2) a relatively stable measurement temperature to maintain radiometric accuracy and enable precise calibration.
Data from martian rovers and martian meteorites indicate the presence of ore minerals. There are three spectrometers, CRISM (Compact Reconnaissance Imaging Spectrometer for Mars; spectral range 0.4-3.9 μm) onboard Mars Reconnaissance Orbiter (MRO), as well as OMEGA (Observatoire pour la Mineralogie, l'Eau, les Glaces et l; Activité, 0.4-5.1 μm ) and PFS (Planetary Fourier Spectrometer, 1.3-45.0 μm) onboard Mars Express (MEX), that operate in the near infrared (NIR) spectrum and provide information on the mineral composition of Mars. None of them, however is already capable to efficiently identify sulfides. Detecting sulfide ore deposits is difficult in NIR due to spectral interferences with silicates. Because of the limited insitu measurements by the Opportunity, Spirit, Curiosity, and Perseverance rovers, Mars mineralogical studies must be supported by studies of terrestrial analogs. One example is the Rio Tinto area in Andalusia, Spain, which hosts the largest known volcanogenic massive sulfide deposits on Earth. In this area, we analyzed satellite images in the NIR spectrum and detected pyrite from the orbit. Landsat 8 Collection 2 Level 2 images (30 m/pixel), ASTER L2 Surface Radiance VNIR and Crosstalk Corrected SWIR (09XT; 15-30 m/pixel), and Sentinel 2 of Level 2a (10-20 m/pixel) habe been used. We have tested several RGB band compositions as well as band maths and band rations. For preliminary pyrite identification we have chosen the following solutions: 1) RGB: 7 6 4, RGB: 5 6 7, RGB: 6 3 2 for Landsat 8; 2) RGB: (5 × 6)/7, (4 × 6)/(5 × 2), (5 × 6)/(7 × 2), RGB: 42, 45, 56, RGB: 1 2 3 for ASTER 09XT; 3) RGB 12 11 2 for Sentinel 2a. Within the selected areas, spectral signatures have been checked and compared to the labolatory patterns. The identified pyrite locations will be then investigated during field studies in Rio Tinto area planned to March 16-28,2022.
<p>Sulfides are the most important group of ore minerals and are especially crucial for copper, silver, and gold. Despite the lack of direct evidence, sulfide ores are anticipated on Mars (Pirajno and van Kranendonk, 2005; West and Clarke, 2010). Rover and orbiter data along with geochemical modeling suggest the presence of pyrite (FeS<sub>2</sub>), marcasite (FeS<sub>2</sub>), and pyrrhotite (Fe<sub>1&#8722;x</sub>S) at the Martian surface (Ehlmann and Edwards, 2014). In addition, Martian meteorites show that the Martian crust is significantly enriched in chalcophile elements compared to the Martian mantle (Wang and Becker, 2017) and host a variety of magmatic and hydrothermal sulfides similar to that on Earth (Baumgartner et al., 2017; Lorand et al., 2018).</p> <p>Infrared spectrometers orbiting Mars with high capabilities to use in mineralogical studies include CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) operating in a wavelength range of 0.4&#8211;3.9 &#181;m onboard Mars Reconnaissance Orbiter (MRO), OMEGA (Observatoire pour la Min&#233;ralogie, l&#8217;Eau, les Glaces et l&#8217;Activit&#233;; 0.4&#8211;5.1 &#181;m) and PFS (Planetary Fourier Spectrometer; 1.3&#8211;45.0 &#181;m) onboard Mars Express (MEX). To date, however, few works were able to localize sulfides from the orbit due to difficult interpretation caused by spectral interferences with common silicates, which are impossible to resolve without ground calibration (Horgan et al., 2014). To overcome this, we have mapped for pyrite content a 500 m x 100 m test field rich in pyrite within the Rio Tinto planetary field analog mining area in Spain for pyrite to compare the obtained results with remote sensing data from the Landsat 8, Sentinel-2, and ASTER satellites (see Ciazela M. et al. this session). The Rio Tinto area hosts the largest known volcanogenic massive sulfide deposits on Earth (Martin-Izard et al., 2015).</p> <p>We have investigated 614 sites along a river bed (Fig. 1) located 3 m from each other. At each site, we investigated 5 random samples for pyrite content. The pyrite content was always estimated by 2 to 4 researchers, and the average for each site was computed. The average pyrite content in the entire investigated area is 7.0 vol.% (12.6 wt.%). We have observed two fields, 30 x 30 m, and 30 x 60 m, with average pyrite contents >50 wt.%, which should be suitable for its detection from the orbit, both with Sentinel-2 (field resolution of 10 m) and Landsat (30 m) (see Ciazela M. et al., this session).</p> <p>Our results will help determine abundance thresholds for the detection of pyrite on Mars and identify its key spectral features for this detection.</p> <p>Acknowledgments: This research is supported by the National Science Centre of Poland project OPUS19 no. 2020/37/B/ST10/01420 and Europlanet2024-research infrastructure grant no. 20-EPN2-020.</p> <p><img src="" alt="" /></p> <p><strong>Figure 1. </strong>The ordinary kriging interpolation maps of pyrite content based on 614 sampling sites.</p> <p>References:</p> <p>Baumgartner R. J., Fiorentini M. L., Lorand J. P., Baratoux D., Zaccarini F., Ferri&#232;re L., Pra&#353;ek M. K. and Sener K. (2017) The role of sulfides in the fractionation of highly siderophile and chalcophile elements during the formation of martian shergottite meteorites. <em>Geochim. Cosmochim. Acta</em> <strong>210</strong>, 1&#8211;24.</p> <p>Ehlmann B. L. and Edwards C. S. (2014) Mineralogy of the Martian Surface. <em>Annu. Rev. Earth Planet. Sci.</em>, 291&#8211;315.</p> <p>Horgan B. H. N., Cloutis E. A., Mann P. and Bell J. F. (2014) Near-infrared spectra of ferrous mineral mixtures and methods for their identification in planetary surface spectra. <em>Icarus</em> <strong>234</strong>, 132&#8211;154.</p> <p>Lorand J. P., Pont S., Chevrier V., Luguet A., Zanda B. and Hewins R. (2018) Petrogenesis of martian sulfides in the Chassigny meteorite. <em>Am. Mineral.</em> <strong>103</strong>, 872&#8211;885.</p> <p>Martin-Izard A., Arias D., Arias M., Gumiel P., Sanderson D. J., Casta&#241;on C., Lavandeira A. and Sanchez J. (2015) A new 3D geological model and interpretation of structural evolution of the world-class Rio Tinto VMS deposit, Iberian Pyrite Belt (Spain). <em>Ore Geol. Rev.</em> <strong>71</strong>, 457&#8211;476.</p> <p>Pirajno F. and van Kranendonk M. J. (2005) Review of hydrothermal processes and systems on Earth and implications for Martian analogues. <em>Aust. J. Earth Sci.</em> <strong>52</strong>, 329&#8211;351.</p> <p>Wang Z. and Becker H. (2017) Chalcophile elements in Martian meteorites indicate low sulfur content in the Martian interior and a volatile element-depleted late veneer. <em>Earth Planet. Sci. Lett.</em> <strong>463</strong>, 56&#8211;68.</p> <p>West M. D. and Clarke J. D. A. (2010) Potential martian mineral resources: Mechanisms and terrestrial analogues. <em>Planet. Space Sci.</em> <strong>58</strong>, 574&#8211;582.</p>
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