Skip to Main Content
Book Chapter

Utility of Magnetic and Gravity Data in Evaluating Regional Controls on Mineralization: Examples from the Western United States

By
T. G. Hildenbrand
T. G. Hildenbrand
U.S. Geological Survey, Mail Stop 989, 345 Middlefield Road, Menlo Park, California 94025
Search for other works by this author on:
Byron Berger
Byron Berger
U.S. Geological Survey, Mail Stop 964, Denver Federal Center, Denver, Colorado 80225
Search for other works by this author on:
R. C. Jachens
R. C. Jachens
U.S. Geological Survey, Mail Stop 989, 345 Middlefield Road, Menlo Park, California 94025
Search for other works by this author on:
Steve Ludington
Steve Ludington
U.S. Geological Survey, Mail Stop 989, 345 Middlefield Road, Menlo Park, California 94025
Search for other works by this author on:
Published:
January 01, 2001

Abstract

Interacting fractures enhance and localize permeability in the Earth's crust and are, therefore, important phenomena in localizing magmatic and hydrothermal systems. The ability to identify where such interactions are present is useful in evaluating likely areas of mineralized rock, particularly in covered terrains. Regardless of map scale, the interpretation of gravity and magnetic data can define deep-seated crustal fractures and faults that may have guided emplacement of igneous rocks and large ore deposits. Here we emphasize recurring regional-scale structural relationships mainly from the western United States based on the interpretation of potential-field data, which can elucidate areas of past and present fluid flow in the crust.

In particular, we explore the utility of regional gravity and magnetic data to aid in understanding the distribution of large Mesozoic and Cenozoic ore deposits (primarily epithermal and pluton-related precious and base metal deposits, and sediment-hosted gold deposits) in the western United States cordillera. On the broadest scale, most ore deposits lie within areas characterized by low magnetization. The Mesozoic Mother Lode gold belt displays characteristic geophysical signatures (regional gravity high, regional low-to-moderate background magnetic field anomaly, long curvilinear magnetic highs) that might serve as an exploration guide. Geophysical lineaments characterize the Idaho-Montana porphyry belt and the La Caridad-Mineral Park belt (from northern Mexico to western Arizona) and, thus, indicate deep-seated control for these mineral belts. At a more local scale, in Nevada, geophysical data define deep-rooted faults and magmatic zones that correspond to patterns of epithermal precious-metal deposits, and that may relate to the Carlin gold trend and the Battle Mountain-Eureka mineral belt. One recurring structural model evolving from this study is that mineralization in the western United States may be localized along strike-slip fault zones where pull-apart basins or releasing bends provided the increased fracture permeability for the migrating ore-forming fluids (e.g., the Butte, Tombstone, Bagdad, and Battle Mountain districts).

Many deposits discussed in the paper appear, at least in part, to be associated with reactivated older faults as well as with faulting contemporaneous with ore deposition. We conclude that at a local scale, structural elements work together to localize mineral deposits within regional zones or belts. Perhaps the greatest utility of regional geophysical data is the identification of structural relationships that help narrow the study area, where more intensive multidisciplinary team studies can be carried out in a concerted effort to evaluate the mineral potential.

You do not currently have access to this article.

Figures & Tables

Contents

Reviews in Economic Geology

Structural Controls on Ore Genesis

Jeremy P. Richards
Jeremy P. Richards
volume-editor
Department of Earth and Atmospheric Sciences University of Alberta Edmonton, Alberta T6G 2E3 Canada
Search for other works by this author on:
Richard M. Tosdal
Richard M. Tosdal
volume-editor
Department of Earth and Atmospheric Sciences University of Alberta Edmonton, Alberta T6G 2E3 Canada
Search for other works by this author on:
Society of Economic Geologists
Volume
14
ISBN electronic:
9781629490212
Publication date:
January 01, 2001

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal