The Silverton caldera complex in southwest Colorado hosts base and precious metals that have been mined since the late 1800s. Extensive mine workings, excellent bedrock exposures, and deeply incised drainages make this area a natural laboratory ideally suited for furthering our understanding of the mineral systems in a volcanic environment. In addition, state-of-the-art geophysical data processing, combined with physical property measurements, allows us to model subsurface changes in magnetization and electrical resistivity, thereby providing a three dimensional model of the mineralization and alteration within Silverton caldera complex. The 3D geologic framework will provide insight into mineral system formation and associated environmental issues.
Science Issue and Relevance
The Paleogene Silverton and San Juan caldera complex in the western San Juan Mountains near Silverton, Colorado provides an opportunity to investigate the shallow to deep geophysical expressions of a highly altered and mineralized epithermal system that formed after caldera formation. The area was the focus of numerous benchmark USGS studies on the processes related to caldera formation, mineralization, and the environmental effects of legacy mining, such as the 2015 release of toxic mine waters
from the Gold King mine. However, little information exists about the hydraulic conductivity through the colluvium, glacial moraine, and bedrock in the study area. This project is leveraging new and existing geophysical data to better understand the subsurface heterogeneities attributed to the origin and flow of acidic, metal-rich fluids. The results should provide a better understanding of shallow processes important for groundwater quality issues. In addition, the project hopes to better understand the "roots" of structures at depth that may have been conduits for hydrothermal fluids and whether they are groundwater flowpaths today or serve as aquitards. Thus, the resulting 3D models will provide insight into the porphyry epithermal system and associated environmental issues.
Methods to Address Issue

To better understand the 3D geologic framework of the Silverton-San Juan caldera complex, the Project intends to:
- construct 3D models of geology and hydrothermal alteration based on existing maps and processed remote sensing data,
- collect physical property measurements (magnetic susceptibility and electrical conductivity) on lithologies that have been hydrothermally altered,
- use state-of-the-art geophysical data processing techniques, combined with physical property measurements, to develop subsurface models showing changes in magnetization and electrical conductivity,
- collect and process magnetotelluric data to image deep structures within the caldera complex, and
- integrate the modelling results into an interpreted geologic model of the caldera complex.
Below are data releases associated with this project.
Magnetic susceptibility measurements on hydrothermally altered rocks in the Silverton caldera, southwest Colorado
Magnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2018
Audiomagnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2019
Hydrologic reconnaissance to identify areas of emergent groundwater, Mineral Creek, near Silverton, Colorado, June 2020
Airborne electromagnetic and magnetic survey data of the San Juan-Silverton Caldera complex, Silverton, Colorado, 2019
Audiomagnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2018
High resolution helicopter-borne magnetic and electromagnetic survey Eureka Graben area, Colorado September 1999
Below are publications associated with this project.
Geophysical data provide three dimensional insights into porphyry copper systems in the Silverton caldera, Colorado, USA
Geological and geophysical data for a three-dimensional view—Inside the San Juan and Silverton Calderas, Southern Rocky Mountains Volcanic Field, Silverton, Colorado
Data visualization
Arrastra Gulch, Silverton, CO 3D Data Viewer
Airborne electromagnetic and magnetotelluric geophysical surveys were conducted from 2018 to 2019 in Arrastra Gulch along the southern margins of the San Juan and Silverton calderas. This scene provides 3-D data integration combining electromagnetic data, geologic and historical mine mapping, and high-resolution drone imagery.
Below are news stories associated with this project.
Below are partners associated with this project.
- Overview
The Silverton caldera complex in southwest Colorado hosts base and precious metals that have been mined since the late 1800s. Extensive mine workings, excellent bedrock exposures, and deeply incised drainages make this area a natural laboratory ideally suited for furthering our understanding of the mineral systems in a volcanic environment. In addition, state-of-the-art geophysical data processing, combined with physical property measurements, allows us to model subsurface changes in magnetization and electrical resistivity, thereby providing a three dimensional model of the mineralization and alteration within Silverton caldera complex. The 3D geologic framework will provide insight into mineral system formation and associated environmental issues.
Simplified geologic map showing location of the Silverton caldera complex. From Yager and Bove, 2002.(Public domain.) Science Issue and Relevance
The Paleogene Silverton and San Juan caldera complex in the western San Juan Mountains near Silverton, Colorado provides an opportunity to investigate the shallow to deep geophysical expressions of a highly altered and mineralized epithermal system that formed after caldera formation. The area was the focus of numerous benchmark USGS studies on the processes related to caldera formation, mineralization, and the environmental effects of legacy mining, such as the 2015 release of toxic mine waters
from the Gold King mine. However, little information exists about the hydraulic conductivity through the colluvium, glacial moraine, and bedrock in the study area. This project is leveraging new and existing geophysical data to better understand the subsurface heterogeneities attributed to the origin and flow of acidic, metal-rich fluids. The results should provide a better understanding of shallow processes important for groundwater quality issues. In addition, the project hopes to better understand the "roots" of structures at depth that may have been conduits for hydrothermal fluids and whether they are groundwater flowpaths today or serve as aquitards. Thus, the resulting 3D models will provide insight into the porphyry epithermal system and associated environmental issues.Methods to Address Issue
Sources/Usage: Public Domain. Visit Media to see details.Intensely altered propylitic rocks (red and yellow) in the Red Mountain mining district, overprinting the regional, propylitically altered igneous rocks (grayish-green), peaks at top of image. View to west.(Credit: Dr. Raymond Johnson, USGS. Public domain.) To better understand the 3D geologic framework of the Silverton-San Juan caldera complex, the Project intends to:
- construct 3D models of geology and hydrothermal alteration based on existing maps and processed remote sensing data,
- collect physical property measurements (magnetic susceptibility and electrical conductivity) on lithologies that have been hydrothermally altered,
- use state-of-the-art geophysical data processing techniques, combined with physical property measurements, to develop subsurface models showing changes in magnetization and electrical conductivity,
- collect and process magnetotelluric data to image deep structures within the caldera complex, and
- integrate the modelling results into an interpreted geologic model of the caldera complex.
- Data
Below are data releases associated with this project.
Magnetic susceptibility measurements on hydrothermally altered rocks in the Silverton caldera, southwest Colorado
The U.S. Geological Survey (USGS) collected magnetic susceptibility measurements on rock outcrops to help understand causative sources of magnetic survey anomalies in the Silverton caldera region, southwest Colorado. A total of 1,400 measurements of magnetic susceptibility from 87 locations have been conducted on Paleogene volcanic and plutonic rocks that have been hydrothermally altered. MagneticMagnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2018
This data release includes magnetotelluric (MT) sounding data collected in July 2018 in the Silverton Caldera complex, Colorado, in the Southern Rocky Mountain Volcanic Field, by the U.S. Geological Survey (USGS). Along with geologic mapping, airborne magnetics, airborne electromagnetics, and audiomagnetotellurics, the USGS collected MT data at 22 sites along four profiles ranging from 3 to 6 kiloAudiomagnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2019
This dataset includes audiomagnetotelluric (AMT) sounding data collected in July 2019 in the Silverton Caldera complex, Colorado, in the Southern Rocky Mountain Volcanic Field, by the U.S. Geological Survey (USGS). Along with geologic mapping, airborne magnetics, airborne electromagnetics, and magnetotellurics, the USGS collected AMT data at 26 sites along five profiles ranging from 2 to 5 kilometHydrologic reconnaissance to identify areas of emergent groundwater, Mineral Creek, near Silverton, Colorado, June 2020
Hydrologic reconnaissance of Mineral Creek near Silverton, Colo., was conducted from June 25-27, 2020. Both banks of Mineral Creek and the adjacent hillsides were walked, starting near the ghost town of Chattanooga and proceeding downstream to the confluence of Mineral Creek with the Middle Fork of Mineral Creek. The purpose of this reconnaissance was to identify areas of emergent groundwater onAirborne electromagnetic and magnetic survey data of the San Juan-Silverton Caldera complex, Silverton, Colorado, 2019
Airborne electromagnetic (AEM) and magnetic survey data were collected during April and May 2019 along 1,467 line-kilometers in the San Juan-Silverton Caldera complex, Colorado, in the Southern Rocky Mountain Volcanic Field. Data were acquired by Geotech, Ltd. with the versatile time-domain electromagnetic (VTEM) system together with a Geometrics optically pumped cesium vapor magnetometer. The surAudiomagnetotelluric sounding data in the Silverton Caldera complex, Colorado, 2018
This data release includes audiomagnetotelluric (AMT) sounding data collected in July 2018 in the Silverton Caldera complex, Colorado, in the Southern Rocky Mountain Volcanic Field, by the U.S. Geological Survey (USGS). Along with geologic mapping, airborne magnetics, airborne electromagnetics, and magnetotellurics, the USGS collected AMT data at 24 sites along four profiles ranging from 3 to 6 kiHigh resolution helicopter-borne magnetic and electromagnetic survey Eureka Graben area, Colorado September 1999
On September 25, 1998, SIAL Gosciences Inc. (SIAL) was awarded Department of Interior, contract 98CRCN1018, by the U.S. Geological Survey. This contract required SIAL to carry out a high-sensitivity magnetic and electromagnetic helicopter survey over one block located in the Eureka Graben Area near Silverton, Colorado. The primary goal of this project was to provide digitally recorded and processe - Publications
Below are publications associated with this project.
Geophysical data provide three dimensional insights into porphyry copper systems in the Silverton caldera, Colorado, USA
The Silverton caldera in southwest Colorado, USA hosts polymetallic veins and pervasively altered rocks indicative of porphyry copper systems. Nearly a kilometer of erosion has exposed multiple levels of the hydrothermal systems from shallow lithocaps down to quartz-sericite-pyrite veins. New airborne electromagnetic and magnetic survey data are integrated with previous alteration mapping and porpAuthorsEric Anderson, Douglas Yager, Maria Deszcz-Pan, Bennett Eugene Hoogenboom, Brian D. Rodriguez, Bruce SmithGeological and geophysical data for a three-dimensional view—Inside the San Juan and Silverton Calderas, Southern Rocky Mountains Volcanic Field, Silverton, Colorado
IntroductionThe 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 forAuthorsDouglas B. Yager, Eric D. Anderson, Maria Deszcz-Pan, Brian D. Rodriguez, Bruce D. Smith - Web Tools
Data visualization
Arrastra Gulch, Silverton, CO 3D Data Viewer
Airborne electromagnetic and magnetotelluric geophysical surveys were conducted from 2018 to 2019 in Arrastra Gulch along the southern margins of the San Juan and Silverton calderas. This scene provides 3-D data integration combining electromagnetic data, geologic and historical mine mapping, and high-resolution drone imagery.
- News
Below are news stories associated with this project.
- Partners
Below are partners associated with this project.