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Overview

geologist examines granitic rocks, Alaska
USGS geologist Erin Todd examines granitic rocks in outcrop before collecting samples for geochemistry and geochronology in Lake Clark National Park, Alaska. Photo by Jamey Jones, USGS.

Alaska hosts a well-documented belt of ore deposits that lies roughly parallel to the Alaska Range, beginning at the Alaska Peninsula in the southwest, continuing up through the Fairbanks Mining District in the north, and curving back into the Tintina Gold Belt on its eastern end. Known mineral prospects and occurrences include porphyry copper, intrusion-related gold, volcanogenic massive sulfides (VMS), and rare earth element (REE) deposits. Both the Range and its associated mineral deposits are spatially and genetically related to the emplacement of igneous rocks caused by subduction of the oceanic Pacific plate beneath the overriding continental Alaska plate.

This project focuses on the Neacola Mountains and surrounding areas in the active volcanic arc on the west side of Cook Inlet, roughly between Chakachamna Lake and Lake Clark. Previous mapping has shown that the region is bisected by the northeast-trending Lake Clark fault; older (Mesozoic) rocks and mineral prospects are exposed to the east of the fault, whereas younger (Cenozoic) rocks and deposits are found to the west. In addition, geophysical surveys have revealed a chain of magnetic anomalies on the western side of the fault, some of which coincide with known mineral deposits. The geology both north and south of the current project area has undergone extensive scrutiny, and this study will fill in the knowledge gaps between the two regions.

In order to understand the tectonic history and mineral resource potential of this section of the arc that bridges the southern Alaska and northern Aleutian ranges, this project seeks to develop a comprehensive geologic framework that encompasses the entire geologic column, from the oldest terrane fragments and basement rocks to the younger igneous and overlapping sedimentary rocks. Detailed field mapping will delineate and differentiate rocks that host mineralization as well as characterize the surrounding sedimentary, igneous, and metamorphic country rocks. Geochemical analyses and age dating will contribute to an understanding of the timing and evolution of subduction-induced magmatism and the distribution and timing of associated mineralizing events. Investigation of the magnetic anomalies and comparison of mineral occurrences in the area to known deposits outside the area will allow an evaluation of potential mineral endowment. The resultant regional synthesis of the geology, geochemistry, and geophysics will lead to a better understanding of the extent, distribution, genesis, and tectonic setting of the host rocks and their attendant mineralized systems.

helicopter approaching for landing
Helicopter approaching for landing to retrieve geologists from a mapping and sampling station west of Redoubt volcano. Photo by Jamey Jones, USGS.

Products

geologists sampling in Alaska
USGS scientists Erin Todd and Jonathan Caine wait for a helicopter pickup at a geologic mapping and sampling station high in the Neacola Mountains, Alaska. Photo by Jamey Jones, USGS.

Abstracts

Jones, J.V. III, and Todd, E., 2016, Variations in tectonic style and setting along the southern Alaska margin since the Jurassic: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-281279. (Invited)

Karl, S.M., Box, S.E., Lease, R.O., Jones, J.V. III, Holm-Denoma, C.S., Bradley, D.C., and Haeussler, P.J., 2016, Independent Jurassic to Late Cretaceous depositional systems defined by sandstone petrography and detrital zircons constrain closure of the Kahiltna-Kuskokwim basin in southern and southwestern Alaska: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-281104.

Lease, R.O., and Haeussler, P.J., 2015, Accelerated erosion of high-latitude glaciated terrain in Alaska since 3-4 Ma: Abstract T33A-2925 presented at 2015 Fall Meeting, AGU, San Francisco, Calif., 14-18 Dec. View Lease AGU abstract.

Todd, E., Jones, J.V. III, and Kylander-Clark, A., 2016, Zircon ages and compositions constrain changes in melt sources during and after progressive accretion of the Wrangellia composite Terrane to the southern Alaska margin: Geological Society of America Abstracts with Programs, Vol. 48, No. 7, doi:10.1130/abs/2016AM-280368. (Invited)

Todd, E., Jones III, J., and Kylander-Clark, A., 2015, Hf isotopes and geochemical evidence constrain the nature and sources of melting during and after progressive accretion of the Wrangellia composite terrane to the southern Alaska margin: Abstract T51C-2897 presented at 2015 American Geophysical Union Fall Meeting, 14-18 December 2015, San Francisco, CA. View Todd AGU abstract.

Partners

Installation of geophysical equipment
USGS scientist Beth Burton and helicopter pilot Drew Rose install geophysical equipment northwest of Lake Clark National Park, Alaska. Photo by Jamey Jones, USGS.

Project Contacts

James V. Jones III
Phone: 907-786-7442
Email: jvjones@usgs.gov
Alaska Science Center

Erin Todd
Phone: 907-786-7441
Email: etodd@usgs.gov
Alaska Science Center

Mineral Resources Program Science Priority

The use of firm, trade, and brand names is for identification purposes only and does not constitute endorsement by the U.S. government.

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