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Metallogenic evolution of Mesoproterozoic sedimentary rocks in Idaho and Montana

Project Objectives

The objectives of this Project were twofold: to understand the processes of base and precious metal mineralization in the large Mesoproterozoic basins in the northern U.S. Cordillera, and to enhance the prediction of potential for undiscovered mineral deposits in this basin.

A major emphasis of this Project was to refine the known Mesoproterozoic geologic framework of the region, both in terms of stratigraphy and sedimentalogy as well as tectonics of basin development. The Mesoproterozoic deposits in this region host important syngenetic stratabound as well as younger epigenetic mineral deposits; the integration of stratigraphic, tectonic, magmatic, and geochronologic studies assist in the development of mineral deposit models that will further enhance our ability to predict potential for undiscovered deposits.

Key to the success of this Project and the accomplishment of the objectives was the synthesis of as much previously accumulated geologic knowledge as possible—stratigraphic, structural, tectonic, geochronologic—that has been obtained, in large part, by the Headwaters Project.

Relevance & Impact

Exploration for undiscovered mineral deposits in the Mesoproterozic rocks of the northwest U.S. has generally followed traditional programs that require extensive geochemical analysis of stream sediments. Little attention has been paid to prediction of the location of mineral deposits based on tectonic controls or deposit type. The Project's intent was to provide greater insight into tectonic controls of mineral deposition and to enhance knowledge of the mineral deposit models that pertain to metallogeny within the Mesoproterozic basins.

The multidisciplinary study of metallogeny in the northern Cordillera provided new interpretations of the crustal evolution that have direct applicability to new interpretations of mineral resource and environmental assessments in the region. Impacts included:

  1. Precambrian basement map, tectonic analysis, and characterization of Paleoproterozoic mineral deposits;
  2. palinspastic and tectonic reconstruction of Mesoproterozoic rift basins and characterization of related sediment-hosted deposit types;
  3. characterization of timing of orogenesis, composition, and magnetic patterns of the crystalline basement terranes give data for recognition of related Laurentian basement fragments now amalgamated into crust of other continents aiding a global understanding of plate tectonics and paleoclimate (Rodinia reconstructions and Snowball Earth events);
  4. tectonic map and analysis of Mesozoic arc-continent oblique collisional zones and translation structures and the characterizition of related mineral deposit types;
  5. model for genesis of very different magmatic systems that resulted in different types of mineral deposits (Atlanta, Boulder, Challis systems) or near total lack of mineral deposits despite same compositions and sequences of magmatism (Bitterroot and Kaniksu batholiths);
  6. integrated tectonic model of northern U.S. Cordillera; and
  7. process-oriented crustal evolution and tectonic setting analyses of mineral deposits with emphasis on Butte, Coeur d'Alene, Montana-Idaho porphyry belt, and sediment-hosted deposits (Blackbird, Spar Lake, etc.) for future resource assessments.

Project Contact

J. Michael O'Neill
Phone:303-236-1288
Email: mnoneill@usgs.gov

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Mineral Resources Program
Eastern Central GMEG Alaska Minerals Information Crustal Geophysics and Geochemistry Spatial Data

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