Crustal Imaging and Characterization Team
Task Contact: Daniel Knepper
The main objectives of this Task are to identify and document the spectral signature of geochemical variations in selected mineral and geoenvironmental settings, identify and document the relationships between surficial mineral occurrences and subsurface geophysical properties, and develop methods for integrating remote sensing data with geochemical and geophysical measurements to address mineral and geoenvironmental issues.
AVIRIS, ASTER, or Landsat TM data for the drainage basins selected by the Central Colorado Assessment Project for geochemical and biological sampling during Fiscal Year 2005 will be processed and analyzed for the presence of iron oxide, clay, carbonate, and sulfate minerals, or mineral groups. Field spectral measurements and samples will be collected to verify the remote sensing data analyses. Georeferenced mineral maps, both hardcopy and digital, will be prepared for each drainage basin. As the results of the geochemical and biological analyses become available, these data will be interpreted with respect to the location and distribution of anomalous mineral patterns within the basins.
Results confirm the accuracy of the AVIRIS mineral identification and goethite grain-size mapping. Patterns of spectral variation associated with a grain size series obtained from powdered pure mineral samples appear to be similar to the spectral variation of alluvial material of various sedimentological grain sizes. This finding is of importance because spatial patterns of soil type and pedogenic maturity, alluvial grain size distributions, and proximity to bedrock outcrops can be determined by spectroscopic remote sensing studies. Samples of hydrothermally altered rocks identified by Tetracorder analysis of AVIRIS data as containing coarse-grained goethite near jarosite-bearing outcrops and finer-grained or thin coats of goethite in the alluvium down gradient from the source outcrops were analyzed visually and spectrally in the laboratory. Results showed that all of the goethite was medium- to coarse-grained and that the grain size differences identified by Tetracorder were actually caused by differences in goethite abundance.
Infiltration of surface water through mine waste can be an important or even dominant source of contaminants in a watershed. The Waldorf mine site in Clear Creek County, Colorado is typical of tens of thousands of small mines and prospects on public lands throughout the United States. In this study, electromagnetic (EM) conductivity and direct current (dc) resistivity surveys were conducted in tandem with a NaCl tracer study to delineate ground-water flowpaths through a mine-waste dump and adjacent wetland area. The tracer was used to tag adit water infiltrating from braided channels flowing over the top of the dump to seeps at the base of the dump. Infiltration beneath the braided channels had a maximum flow rate of 92 m/day and a hydraulic conductivity of 1.6 x 104 cm3/s. After rerouting of adit flow around the waste dump, discharge at some of the largest seeps was reduced , although not all seepage was eliminated entirely. By integrating the results of the tracer study with those of the EM and dc geophysical surveys, two main flowpaths of ground-water movement were identified (1) beneath the dump and (2) through the dump. The main source of water to the first flowpath is deeper ground water emerging from the fault zone beneath the collapsed adit. This flowpath travels beneath the waste dump and appears to have been unaffected by rerouting of the adit discharge around the waste dump. The source of the second flowpath is infiltration of adit water from braided channels flowing over the top of the dump, which is intermediate in depth and flows through the center of the waste dump. Following rerouting of adit flow, discharge to seeps at the toe of the dump along this flowpath was greatly reduced by as much as two thirds, although not eliminated entirely. Improved understanding of ground-water flowpaths through this abandoned mine site has important implications toward developing effective remediation strategies to target sources of metals emanating from the adit, waste dump, and contaminated wetland area.
During fiscal year 2005, it was discovered that natural color Landsat TM images provided a means of mapping the distribution of a late Miocene erosion surface in the Colorado Front Range. Preliminary mapping suggested that the erosion surface is offset along young faults that are characterized by anomalous topography and stream patterns. Using image processing and display techniques on digital elevation data greatly helps to locate and map the young faults. Recognition of these young faults is important to the understanding of variations in mineralization and hydrothermal alteration patterns in terms of level of emplacement and level of erosion. These questions are fundamental to assessing the mineral potential of an area.
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