T142 Geologic Mapping in the Twenty-First Century: Innovative Applications of Technology and Strategies to Aid Field-Based Studies

Monday, 5 November 2018
1:30 PM - 5:30 PM
Room 242

PROGRESS TOWARDS CONSTRUCTING A 3-DIMENSIONAL GEOLOGICAL AND GEOPHYSICAL MODEL OF THE SAN JUAN AND SILVERTON CALDERAS, OURAY, SAN JUAN, AND SAN MIGUEL COUNTIES, COLORADO

Paper number: T142-14
Program: Technical Sessions
Time: 4:45 PM – 5:00 PM

Authors

Abstract

The U.S. Geological Survey is integrating geological and geophysical data to build a shallow (10s of meters) to deep (> 5 km), 3-D model of the San Juan - Silverton caldera complex. Published maps of the study area provide bedrock, structure, alteration, surficial geology and selected mine tunnel inputs to the model. Advances in geophysical data processing allow for reevaluation of legacy airborne electromagnetic and magnetic data to help map subsurface lithologies and alteration types, which will be combined with surface mapping and mine tunnel datasets. In this geologic environment, electromagnetic and magnetic survey data have approximate depths of investigation of 10s of meters and 5 km, respectively. These data will be used to map electrically conductive features such as faults, sediments, hydrothermal alteration, and conductive groundwater flow paths. Preliminary results show some high conductivity anomalies may be caused by enriched metal concentrations in groundwater from shallow (few meters) and deeper (10s of meters) flow paths along perennial streams. In addition, the electromagnetic data provide conductivity depth profiles along streams highlighting electrically conductive groundwater flow paths that can complicate mine cleanup. Rock magnetic susceptibility field measurements near epithermal vein systems and adjacent to intrusions demonstrate where hydrothermal alteration events were magnetite destructive. Magnetotelluric data collected in July 2018, imaging resistivity changes to depths greater than 5 km show conductivity contrasts across caldera structures that may be interpreted as Paleogene hydrothermal flow paths that led to mineralization in the caldera complex. These data also help image electrical conductivity changes at intermediate depths (100s of meters) beneath the capabilities of the airborne electromagnetic data. The results provide insights into identifying concealed mineral deposits in similar geologic settings. Ultimately, the holistic model will provide a robust 3-D geologic framework, which can be used by land management agencies to make better informed decisions pertaining to abandoned mine lands reclamation and help to advance the understanding of the geoenvironmental conditions and economic potential of a mineralized caldera complex.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321159

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