Remediation of Abandoned Mine Lands

Thursday, October 2, 2008 : 11:20 a.m.

Airborne Hyperspectral Mapping of An Acid Mine Drainage Analog, Central Colorado

David W. Coulter, Ph.D., Overhill Imaging and Cartography LLC, Matthew A. Sares, Colorado Geological Survey, Phoebe L. Hauff, Spectral International Inc., Douglas C. Peters, Peters Geosciences, David A. Bird, Colorado Division of Reclamation, Mining & Safety, Fredrick B. Henderson III, Ph.D., Hendco Services and Eric C. Prosh, Ph.D., Government of Nunavut

Acid mine drainage usually is measured and characterized in systems that have been active for a relatively short period.  Whereas most mines are newer than a few hundred years, natural acid drainage systems exist which have been active for much longer periods of time.  East and West Red mountains in the Grizzly Peak Caldera of Colorado are just such systems.  These exposed high sulfide bearing porphyries generate significant acid drainage.  They are situated in high terrain and are continuously eroded to expose fresh sulfides to oxidation much as mining activity exposes sulfides through excavation.  The surface and downstream impacts have been developing since the retreat of the Pinedale glaciers approximately 6000 years ago.  Although some exploration activities have altered the surface morphology slightly, the patterns of acid drainage mineralogy are interpreted to be dominated by natural processes.

This study utilizes airborne hyperspectral imagery to map the surface mineralogy of these systems.  The hyperspectral imagery is composed of 227 bands which finely sample the reflected light between 446 nanometers and 2441 nanometers for each pixel.  It was flown with a spatial resolution of 2.5 meters.  The spectroscopy of each pixel is analyzed to determine the mineralogical composition of the surface.  Jarosite, goethite, hematite, illite, kaolinite and dickite are mapped.  Furthermore, spectral unmixing approaches are utilized to map the relative concentrations of these minerals.

The results of the analyses show that acidic seeps and springs are identified by the concentration of jarosite relative to goethite and hematite and that these minerals are distinctly zoned.  Some of the identified seeps are very subtle and not apparent in the field.  The clay mineralogy also appears to reflect the presence of acidic ground waters.  Although shown in the context of a natural system, the technology is applicable to mine waste monitoring and characterization.

David W. Coulter, Ph.D., Overhill Imaging and Cartography LLC Dr. Coulter has been involved in remote sensing for exploration and mining for over 25 years. He was Manager of Remote Sensing at Newmont Mining Corporation from 1985 to 2001. His focus is on exploiting hyperspectral and multispectral imagery for generating exploration targets. From 2002 to 2006 he was involved in the use of hyperspectral imagery to map anthropogenic and natural acid drainage in the Leadville District and Grizzly Peak Caldera in Colorado for a NASA funded project managed by the Colorado Geological Survey. He earned a Ph.D. from the Colorado School of Mines in 2006 based on this work.


Remediation of Abandoned Mine Lands