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Alaska Mineral Resources

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Regional Geologic, Geochemical, Geophysical, and Mineral Deposit Data for Economic Development in Alaska in the 21st Century

    Seward Peninsula base-metal resources

    Photo of USGS geologists at outcrop of Nome Group metasediments near Pilgrim River on the Seward Peninsula

    Since the gold rush of the late 19th century, it has been recognized that the mineral endowment of Alaska's Seward Peninsula is considerable. The well-known placer gold operations have had significant historic production and continue operating to this day. Lode gold production has also occurred. The potential for base-metal deposits (Pb, Zn, Cu) has attracted exploration to the peninsula for decades, but the extent of that resource is unknown. Scattered across the Seward Peninsula, in an area 150 x 200 km, are numerous prospects and occurrences of stratiform massive sulfides. This task is evaluating whether these occurrences represent a group of unrelated, small occurrences with limited resource potential, or a large, regional mineralizing system that could have produced a significant base-metal resource.

    To evaluate the age, extent, tectonic, and metallogenic affinities of any syngenetic stratiform mineralization hosted by the Nome Group, researchers are applying appropriate geochronologic and paleontologic methods to better define the age of the protolith of Nome Group metasedimentary and meta-igneous units and to determine the age of any syngenetic base-metal occurrences. They are determining the geochemical characteristics of Nome Group units, related basement, and subunits that host syngenetic base-metal sulfide mineralization. Methods include (i) identifying the isotopic characteristics and affinities of base-metal occurrences, possible regional aquifers, and likely basement metal source rocks to the Nome Group succession and (ii) determining geochemical (major, minor, trace, and isotopic) characteristics of mafic meta-igneous rocks contained within the Nome Group in order to define the tectonic setting in which those rocks were formed.

    So far, results from geochronologic investigations indicate that the protoliths of the Nome Group included more Silurian or Devonian rocks and fewer Late Proterozoic rocks than previously thought; most of the Nome Group protoliths are early Paleozoic in age. Metabasaltic rocks that are part of the Nome Group package likely formed during incipient rifting of continental crust, but the timing of the rifting event has yet to be determined. Isotopic analyses of rocks from select base-metal occurrences are consistent with an early Paleozoic age for mineralization.



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