Registration for the MN Section of AIPG March 1st Luncheon is open online. The cost is $21 for non-members and $16 for members. Students may attend free of charge. Online registration ends Monday, February 29th at 1:00 PM. Same-day luncheon registration cost is $25.

PRESENTATION TITLE

The Soudan Mine as a Mars Analog

by E. Calvin Alexander, Jr., Morse-Alumni Professor Emeritus, Earth Sciences Department, University of Minnesota

PRESENTATION OVERVIEW

The Soudan Iron Mine in northeastern Minnesota mined high grade hematite from the late 1800s until about 1960 in 2.7 billion year old rocks. Unlike the huge open pit mines on Minnesota “Iron Range”, the Soudan was an underground mine working a near vertical ore body. When the mine ceased operations the bottom, 27^th level was 2341ft. below the land surface or 689 feet below sea level. The mine was given to the State of Minnesota and continues operations as State Historic Park offering mine tours to visitors. Physicists from the University of Minnesota have conducted experiments in the mine for several decades. The mine is also a major bat hibernaculum. A calcium, sodium, magnesium chloride brine about twice as salty as sea water seeps into the lowest level of the Soudan Mine. That brine is anoxic and has about 150 ppm of ferrous iron in solution. When those anoxic waters reach the atmosphere in the mine they begin to adsorb oxygen and, mediated by a flourishing microbiology, are actively depositing a wide variety of classic cave formations: flow stones, stalagmites, soda straw stalactites and rimstone dams. These formations are made of the iron oxides ferrihydrite and goethite and contain the mineral jarosite – and are spectacularly colored.           

Starting with the earliest Mariner flyby missions to Mars, photographs of surface features apparently produced by liquid water have increased in number, resolution and credibility. The apparently fundamental problem that “liquid water is not stable at the current temperature and pressure of the Martian surface” has been a major obstacle to the scientific credibility the otherwise obvious presence of water produced features on Mars. The observation that the current surface temperature and pressure of Mars is below the triple point of water is valid only for pure water. The triple point of concentrated brine solutions is well within the observed range of Martin water vapor pressures and temperatures. Concentrated brines can exist as stable liquids on significant parts of the Martian surface for significant fractions of each Martian year.           

The “gullies” discovered on Mars by the high resolution MOS orbiter camera have been confirmed by the higher resolution HiRISE orbiter images and are now known to occur widely on Mars. In several locations on Mars the MOS and HiRISE images reveal structures that appear to be rimstone dams associated with the distal ends of gullies.           

The presence of iron oxide rimstone dams growing from the brines in the Soudan Mine suggest that those brines may be an analog for conditions on some parts of Mars. It is interesting to note that in the Soudan Mine brines form a productive environment for several microbiological communities.

SPEAKER BIOGRAPHY

Calvin Alexander was born and raised in Oklahoma. He graduated with a BS in Chemistry from Oklahoma State University in May 1966. While an undergraduate at OSU he developed a sport interest in cave exploration. He graduated with a PhD in Chemistry from the University of Missouri at Rolla in January 1970. In February 1970 Calvin accepted a position as a post-Doctorial researcher in the Physic Department at the University of California at Berkeley where he was part of the Apollo Lunar Sample Analysis effort. In September 1973 he joined the faculty of the Geology and Geophysics (now Earth Sciences) Department at the University of Minnesota in Minneapolis. His initial research efforts focused on the early history of the solar system and chronology. Calvin’s early sport caving hobby morphed into a major research interest in Karst Hydrogeology in the late 1970s and early 1980s. Much of his research and teaching in the last three decades has focused on how the human species interacts with karst hydrogeology. He retired in May 2014 after 41 years of teaching and research. He remains the Curator of Meteorites for the Earth Sciences Department of the University and is still active in research on meteorites and karst hydrogeology.