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Open-File Report 2010-1076

Distribution of Potential Hydrothermally Altered Rocks in Central Colorado Derived From Landsat Thematic Mapper Data: A Geographic Information System Data Set

By Daniel H. Knepper, Jr.

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As part of the Central Colorado Mineral Resource Assessment Project, the digital image data for four Landsat Thematic Mapper scenes covering central Colorado between Wyoming and New Mexico were acquired and band ratios were calculated after masking pixels dominated by vegetation, snow, and terrain shadows. Ratio values were visually enhanced by contrast stretching, revealing only those areas with strong responses (high ratio values). A color-ratio composite mosaic was prepared for the four scenes so that the distribution of potentially hydrothermally altered rocks could be visually evaluated. To provide a more useful input to a Geographic Information System-based mineral resource assessment, the information contained in the color-ratio composite raster image mosaic was converted to vector-based polygons after thresholding to isolate the strongest ratio responses and spatial filtering to reduce vector complexity and isolate the largest occurrences of potentially hydrothermally altered rocks.

First posted May 14, 2010

For additional information contact:

USGS Central Mineral and Environmental Resources Science Center
Box 25046, MS-973
Denver Federal Center
Denver, CO 80225

http://minerals.cr.usgs.gov/

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Suggested citation:

Knepper, D.H., Jr., 2010, Distribution of potential hydrothermally altered rocks in central Colorado derived from Landsat Thematic Mapper data: A geographic information system data set: U.S. Geological Survey Open-File Report 2010-1076, 14 p.



Contents

Abstract

Introduction

Image Processing and Interpretation

Filtering and Conversion to Vector Polygons

Characteristics of Potential Alteration Shapefile (TM_potential_alteration.shp)

References Cited


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