Geological and geophysical data for a three-dimensional view—Inside the San Juan and Silverton Calderas, Southern Rocky Mountains Volcanic Field, Silverton, Colorado

Fact Sheet 2019-3026
Prepared in collaboration with U.S. Forest Service, Bureau of Land Management, U.S. Environmental Protection Agency, Colorado Division of Reclamation Mining and Safety, Colorado Department of Public Health and Environment, and Animas River Stakeholders Group
By: , and 

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Introduction

The San Juan-Silverton caldera complex located near Silverton, Colorado, in the Southern Rocky Mountains volcanic field is an ideal natural laboratory for furthering the understanding of shallow-to-deep volcanic-related mineral systems. Recent advances in geophysical data processing and three-dimensional (3D) model construction will help to characterize shallow properties important for understanding surface water and groundwater quality issues and will also improve knowledge of deep geological structures that may have been conduits for hydrothermal fluids that formed mineral deposits. The study has general applications to mineral resource assessments in other areas of the world and to identifying possible groundwater flow paths and associated geochemistry important in abandoned mine lands cleanup.

Silverton, Colorado, is the site of a spectacular succession of igneous rocks that formed beginning about 35 million years ago (Ma). Base metals (copper, lead, and zinc) and precious metals (silver and gold) mined from the late 1870s to 1991 owe their existence to a 25-million-year cycle of igneous activity. The presence of economic, base, and precious metal deposits within a complex geological setting were largely responsible for stimulating studies by the U.S. Geological Survey (USGS) conducted during the early 20th century. The focus of investigations in the late 20th and 21st centuries have broadened in scope to include abandoned mine lands (AML) investigations. The legacy of hard rock mining in headwater catchment areas caused environmental challenges for local communities and downstream water resource users. The Gold King Mine, located a few kilometers north of Silverton, illustrates the potential environmental effects of abandoned mines. On August 5, 2015, during reclamation efforts at the Gold King Mine, a breach of collapsed workings sent approximately 3 million gallons of acidic and metal-rich mine water into the upper Animas River, a tributary to the Colorado River Basin. Mining-related sources of metals and acidity add to geological sources of metals in surface water and groundwater. Weathering processes of altered and mineralized rock have been a source of acid rock drainage that have been ongoing for millennia.

Suggested Citation

Yager, D.B., Anderson, E.D., Rodriguez, B.D., Deszcz-Pan, M., and Smith, B.D., 2019, Geological and geophysical data for a three-dimensional view—Inside the San Juan and Silverton calderas, Southern Rocky Mountains volcanic field, Silverton, Colorado: U.S. Geological Survey Fact Sheet 2019-3026, 4 p., https://doi.org/10.3133/fs20193026.

ISSN: 2327-6932 (online)

ISSN: 2327-6916 (print)

Study Area

Table of Contents

  • Introduction
  • What is a Caldera?
  • Data For Developing a 3D Model
  • Electromagnetic Data
  • Magnetotelluric Data
  • Summary
  • References

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Geological and geophysical data for a three-dimensional view—Inside the San Juan and Silverton Calderas, Southern Rocky Mountains Volcanic Field, Silverton, Colorado
Series title Fact Sheet
Series number 2019-3026
DOI 10.3133/fs20193026
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Geology, Geophysics, and Geochemistry Science Center
Description 4 p.
Country United States
State Colorado
County San Juan County
Online Only (Y/N) N