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GMEG - Geology, Minerals, Energy, & Geophysics Science Center

Geologic Framework of the East-Central Alaska Mineral Resource Frontier


Project status is complete. Please check the project list for currently active projects

Project Lead: Cynthia Dusel-Bacon - (650) 329-5719 -

Alaska is an important component of the mineral resource potential of the U.S., yet much of its framework geology and base- and precious-metal endowment is still poorly known. This project will produce three publications, based on previous research, that present and interpret important geologic, petrologic, metallogenic, thermochronologic, and geochronologic data for key areas in east-central Alaska. The publications include:

Apatite-fission-track (AFT) dating in the western Fortymile region and implications for the timing of uplift, denudation, and faulting and their relationship, if any, to mineralization.

    • This product will provide important regional tectonic constraints for eastern Alaska where hard to interpret Tertiary apatite fission track cooling ages have been documented. The origin of the post-69-Ma heating/burial event in east-central Alaska is unknown but may be related to continental-scale upper plate magmatism, sedimentation, and deformation above shallow-slab subduction emanating from southern Alaska in the Paleocene. Uplift and tilting documented by the AFT data may have been related to far-field movement on the Denali and Tintina dextral faults. If substantiated, our current hypothesis that attributes burial, heating, and resetting of apatite systematics in Late Cretaceous and older rocks to a blanket of early Tertiary sedimentary and (or) volcanic rocks that was subsequently eroded and deposited in adjacent nonmarine basins will be a highly significant and completely new aspect of the geologic history of east central Alaska.

TIMS U-Pb zircon geochronology and whole-rock major, minor, and trace-element geochemistry for Paleozoic igneous rocks from the eastern Fortymile mining district.

    • This product provides important framework information for the district. Understanding the nature, affinity, and history of Paleozoic magmatism in east-central Alaskan has practical benefits for mineral exploration. Devonian-Mississippian magmatism was widespread throughout the pericratonic tectonic assemblages of the northern Cordillera and many of assemblages contain VMS or SEDEX base-metal mineral deposits. Although these U-Pb ages were listed in a table in our summary chapter on the Paleozoic and metallogenic evolution of pericratonic rocks in east-central Alaska and adjacent Yukon, the geochronology and geochemical data for the Alaska–Yukon border area havenot been published, nor have the results been integrated with the results of our current study in the western part of the Fortymile mining district or with discoveries made during ongoing mining exploration in the adjacent Yukon.

The host rocks and metallogeny of the Sheep Creek syngenetic Zn-Pb-Ag-Sn massive sulfide prospect.

    • This publication will elucidate the metallogenesis of this carbonaceous and siliceous metasedimentary-hosted prospect and its spatial and temporal relationship to nearby VMS deposits in the district. Industry continues to show interest in exploration of the Bonnifield district and this paper will allow proprietary data, made available to the USGS by the Kennecott Mining Company, to be in the public domain.

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