Tuesday, February 21, 2017 GSA Luncheon

"Geologic mapping in the Talkeetna Mountains and Eastern Alaska Range: A story of mineralization and deformation"

Noon Luncheon 11:30-1:00 pm

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The Wrangellia terrane extends through the Eastern Alaska Range and Talkeetna Mountains as a narrow belt of rocks bordered by the Denali, Broxson Gulch, and Talkeetna fault systems to the north, and by the Strelna metamorphic complex to the south. This belt of rocks has been the target of exploration for nickel, copper and platinum-group-element deposits hosted by mafic to ultramafic intrusions related to the Late Triassic Nikolai Greenstone metabasalts. Exploration efforts have faced a number of challenges, including a lack of regional geologic mapping showing the location of prospective intrusions, and a lack of detailed work resolving the specific magmatic architecture of the larger intrusions. Multiple episodes of poorly resolved post-Triassic faulting add further complications.

In an effort to foster exploration success, the Alaska Division of Geological & Geophysical Surveys (DGGS) has invested in a multi-year, multi-disciplinary effort to improve the geologic knowledge of this area through geological mapping. This talk will show how the DGGS blends traditional ‘hammer and compass’ techniques with modern geochemical and geophysical technologies to address formation of mineralization during the Late Triassic, and how these rocks have been affected by tectonic events including the Jurassic amalgamation of Wrangellia and the Peninsular terranes, Cretaceous accretion and translation of Wrangellia with North America, and the ongoing uplift of the Alaska Range.

Left: The 23-km-long, 700-m-thick, Butte Creek multi-phase gabbroic to ultramafic intrusive complex in the northwestern Talkeetna Mountains. Right: Thrust faulting related to Alaska Range uplift puts Late Triassic picrite volcanic rocks on top of Tertiary sedimentary rocks in the Rainy Creek area of the eastern Alaska Range.


Speaker: Evan Twelker - Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska

Evan Twelker joined the Mineral Resources Section of the DGGS in 2013. A native of Fairbanks and Juneau, he received his B.A. from Middlebury College and his M.S. in geology from the University of Alaska Fairbanks under Professor Rainer Newberry. Evan has explored throughout Alaska, working in a variety of geologic settings and deposit types including the Ambler District, the Seward Peninsula, Greens Creek Mine, Livengood, the Pebble area, and the Galore Creek area of northwestern British Columbia. In his role at the DGGS, Evan specializes in bedrock mapping for the purpose of understanding Alaska's metallic mineral resources, and using geological, geophysical, and geochemical data to understand the formation of mineral deposits in space and time. His current focus is on magmatic Ni-Cu-PGE mineralization hosted by the Wrangellia terrane in central Alaska.


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