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Techniques and Methods 11–C5

Analyzing Legacy U.S. Geological Survey Geochemical Databases Using GIS—Applications for a National Mineral Resource Assessment

By Douglas B. Yager, Albert H. Hofstra, and Matthew Granitto

Thumbnail of and link to TM11-C5 documentAbstract

This report emphasizes geographic information system analysis and the display of data stored in the legacy U.S. Geological Survey National Geochemical Database for use in mineral resource investigations. Geochemical analyses of soils, stream sediments, and rocks that are archived in the National Geochemical Database provide an extensive data source for investigating geochemical anomalies. A study area in the Egan Range of east-central Nevada was used to develop a geographic information system analysis methodology for two different geochemical datasets involving detailed (Bureau of Land Management Wilderness) and reconnaissance-scale (National Uranium Resource Evaluation) investigations. ArcGIS was used to analyze and thematically map geochemical information at point locations. Watershed-boundary datasets served as a geographic reference to relate potentially anomalous sample sites with hydrologic unit codes at varying scales. The National Hydrography Dataset was analyzed with Hydrography Event Management and ArcGIS Utility Network Analyst tools to delineate potential sediment-sample provenance along a stream network. These tools can be used to track potential upstream-sediment-contributing areas to a sample site. This methodology identifies geochemically anomalous sample sites, watersheds, and streams that could help focus mineral resource investigations in the field.

First posted May 24, 2012

For additional information contact:
USGS Central Mineral and Environmental Resources Science Center
Box 25046, Mail Stop 973
Denver, CO 80225
minerals.cr.usgs.gov

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Suggested citation:

Yager, D.B., Hofstra, A.H., and Granitto, Matthew, 2012, Analyzing legacy U.S. Geological Survey geochemical databases using GIS—Applications for a national mineral resource assessment: U.S. Geological Survey Techniques and Methods 11–C5, 28 p.



Contents

Abstract

Introduction

Data Sources and Methodology

Digital Mapping Methods

Symbolizing Raw Point Data

Establishing Geochemical Threshold Values

Thematic Mapping of Point-Geochemical Data

Thematic Mapping of Watershed Boundary Datasets Using Point-Geochemical Data

Sediment Provenance

Hydrography Event Management Tools

Geologic Attributes of Anomalous National Hydrography Dataset Streams and Watershed Boundary Datasets

Alluvial Fans

Geospatial Statistics of Point Data

Discussion

Conclusions

Acknowledgments

References Cited

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