Metallogeny and Tectonics of the Lake Clark and Neacola Mountains Region, South-central Alaska

Science Center Objects

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.

Return to Geology

Scientists wait for a helicopter pickup at a geologic mapping and sampling station high in the Neacola Mountains, 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.
​​​​​​​(Credit: Jamey V. Jones III, USGS. Public domain.)

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 arriving to move geologists from Redoubt Volcano, Alaska

Helicopter arriving to pick up geologists after retrieving geophysical equipment from the flanks of Redoubt Volcano, Alaska, July 2015.
(Credit: Jamey Jones, U.S. Geological Survey. Public domain.)