[Paper Review] SWIR Investigation of sites of astrobiological interest

A. J. Brown, Malcolm R. Walter+1 more|arXiv (Cornell University)|Jan 20, 2014

Geochemistry and Geologic Mapping58 references11 citations

TL;DR

This study demonstrates the effectiveness of short-wave infrared (SWIR) spectroscopy using the PIMA instrument for in situ mineralogical analysis at astrobiologically relevant sites. At the Archean Strelley Pool Chert in Western Australia, SWIR detected dolomite, micas, chlorite, and pyrophyllite, indicating past hydrothermal activity and acidic, sulfur-rich conditions—key for assessing Mars analog environments and guiding future rover missions.

ABSTRACT

Rover missions to the rocky bodies of the Solar System and especially to Mars require light- weight, portable instruments that use minimal power, require no sample preparation, and provide suitably diagnostic mineralogical information to an Earth-based exploration team. Short-wave infrared (SWIR) spectroscopic instruments such as the Portable Infrared Mineral Analyser (PIMA, Integrated Spectronics Pty Ltd., Baulkham Hills, NSW, Australia) fulfill all these requirements. We describe an investigation of a possible Mars analogue site using a PIMA instrument. A survey was carried out on the Strelley Pool Chert, an outcrop of stro- matolitic, silicified Archean carbonate and clastic succession in the Pilbara Craton, interpreted as being modified by hydrothermal processes. The results of this study demonstrate the ca- pability of SWIR techniques to add significantly to the geological interpretation of such hy- drothermally altered outcrops. Minerals identified include dolomite, white micas such as il- lite-muscovite, and chlorite. In addition, the detection of pyrophyllite in a bleached and altered unit directly beneath the succession suggests acidic, sulfur-rich hydrothermal activity may have interacted with the silicified sediments of the Strelley Pool Chert.

Motivation & Objective

• To evaluate the utility of portable SWIR spectroscopy for in situ mineral analysis at astrobiologically relevant terrestrial sites.
• To assess whether SWIR can detect mineralogical signatures of hydrothermal alteration in ancient, silicified sediments.
• To identify diagnostic minerals indicative of past hydrothermal activity relevant to Mars exploration.
• To support the development of lightweight, low-power instruments for future planetary rovers.
• To validate SWIR techniques as a diagnostic tool for Earth-based teams interpreting field data from extraterrestrial missions.

Proposed method

• A portable Short-Wave Infrared (SWIR) spectrometer (PIMA) was used to collect in situ spectral data from the Strelley Pool Chert outcrop.
• Spectral data were analyzed to identify mineral phases based on characteristic absorption features in the 1000–2500 nm range.
• Mineral identification was validated using known spectral libraries and field observations of rock textures and alteration patterns.
• The instrument was operated in a field setting without sample preparation, simulating conditions for planetary rovers.
• Data were collected from a hydrothermally altered unit beneath a stromatolitic succession to assess mineralogical changes.
• Spectral features associated with phyllosilicates (e.g., micas, chlorite) and aluminosilicates (e.g., pyrophyllite) were specifically targeted.

Experimental results

Research questions

• RQ1 Can SWIR spectroscopy detect mineralogical indicators of hydrothermal activity in ancient, silicified sedimentary rocks?
• RQ2 What mineral assemblages are present in the Strelley Pool Chert, and what do they reveal about past hydrothermal conditions?
• RQ3 How effective is a lightweight, portable SWIR instrument like PIMA in identifying astrobiologically relevant minerals without sample preparation?
• RQ4 Can SWIR data improve geological interpretation of hydrothermally altered outcrops in Mars analog environments?
• RQ5 What evidence does SWIR provide for acidic, sulfur-rich hydrothermal systems in Archean sedimentary sequences?

Key findings

• Dolomite was identified in the Strelley Pool Chert, indicating carbonate-rich, possibly alkaline hydrothermal conditions.
• White micas such as illite-muscovite were detected, suggesting low-temperature alteration processes.
• Chlorite was identified, consistent with moderate-temperature hydrothermal alteration of silicate minerals.
• Pyrophyllite was detected in a bleached, altered unit beneath the main succession, indicating acidic, aluminum- and silica-rich hydrothermal fluids.
• The presence of pyrophyllite supports the interpretation of sulfur-rich, low-pH hydrothermal activity interacting with silicified sediments.
• SWIR spectroscopy successfully identified key mineral phases in situ with no sample preparation, validating its utility for planetary exploration.