NASA Astrobiology Institute (NAI)

1. High Lake Gossan deposit: An Arctic analogue for ancient Martian surficial processes?

   Project Investigators: Tullis Onstott

   Other Project Members

   Dan McGown (Doctoral Student)

   Logan West (Undergraduate Student)

   Summary

   The massive sulfide deposit at High Lake is covered by a ~1 meter thick layer of Fe oxides and sulfate minerals. The minerals have formed within the last 8,000 years in the active zone of the permafrost and as such the site provides a good analog to those terranes on Mars that contain similar mineral assemblages, e.g. Terra Meridiana, and may have formed under similar, acidic conditions. The minerals present in the High Lake gossan were characterized by XRD, SEM and Mössbauer.

   Astrobiology Roadmap Objectives:

   • Objective 2.1: Mars exploration
   • Objective 5.1: Environment-dependent, molecular evolution in microorganisms
   • Objective 5.2: Co-evolution of microbial communities
   • Objective 5.3: Biochemical adaptation to extreme environments
   • Objective 6.1: Environmental changes and the cycling of elements by the biota, communities, and ecosystems
   • Objective 7.1: Biosignatures to be sought in Solar System materials

   Project Progress

   High Lake Gossan deposit: An Arctic analogue for ancient Martian surficial processes?

   Gossan samples collected during two expeditions to High Lake in Nunavut, Canada, were analyzed to determine their mineral components in order to define parameters for the geochemical environment in which they formed. The gossans represent a natural acid drainage site in an arctic environment that serves as an analogue to the conditions under which sulfate and Fe-oxide formed on Mars. Rock and soil samples were taken from three different outcrops and analyzed using XRD, SEM/EDS, and, in collaboration with R.V. Morris of Johnson Space Center, Mössbauer. Two main mineral assemblages were observed. The first assemblage, which was found primarily in samples from the first outcrop, contained chlorite, phosphate, Fe-oxide, talc and quartz. The second assemblage, which was found at the second and third outcrops, was primarily quartz, mica and jarosite. One sample (G41), which contained Fe-oxide, jarosite and the only observed appearance of gypsum, appears to be transitional between an Fe-oxide dominant assemblage to a jarosite dominant assemblage. Thermodynamic equilibrium with water from seasonal snow melt predicts that the gossan pore water should range from highly acidic and sulfate-rich (pH 0.5-3; SO₄ > 3000mg/l) for the second mineral assemblage to mildly acidic, less sulfate-rich (pH 3-6; SO₄ < 1000mg/l) for the first assemblage. The High Lake gossan differs from acid mine drainage sites located in temperate regions by its lack of diverse sulfate species and smaller crystal sizes. The smaller crystal size may reflect the slower reaction rates at colder temperatures and the seasonal water saturation. These initial results indicate that the High Lake gossan deposit does record mechanisms for which minerals like hematite, goethite, gypsum and jarosite, which are found on Mars, can form in an environment that involves seasonal water occurrence in a cold climate. A manuscript describing these results has been submitted to Planetary and Space Science.

   
   

   Orange and red soils containing diverse iron oxides and sulfates are characteristic of the gossan on the High Lake mine property.

   
   

   Brightly-pigmented oxides can be seen coating the rocky rubble and fine-grained sediment in the gossan at High Lake.

   Field Expeditions

   Name

   High Lake

   Dates

   7/15/07 - 8/15/07

   Location

   Description

   Gossan samples were collected from natural outcrops at the High Lake mining property, Nunavut Territory, Canada. Samples were collected from the surface down to a depth of about 1 meter below the surface.

   Cross-Team Collaborations

   R.V. Morris (Johnson Space Center) collaborated on the characterization of minerals in the High Lake gossan using Mossbauer spectroscopy.

Publications

West, L.  (2008).  Gossan Mineral Relationships at High Lake, Nunavut, Canada: Local Geochemical Inference and Implications as a Martian Analog Site.  AbSciCon.  Santa Clara CA.