The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
North of 60 Mining News - January 3, 2025
Alaska Energy Metals tests the Odie target at the Nikolai nickel-copper-cobalt-PGM project along the Denali Fault.
Map shows the epicenter of a magnitude 7.9 earthquake along the Denali Fault in 2002.
The Denali Fault is easily recognizable as an arc that runs through the epicenter of the 2002 Denali Earthquake.
This image reconstructs the Denali Fault based on key markers (red and orange stars). The left image shows the current location of the sites of the Southcentral Alaska and southern Yukon sites sampled by Regan. The right image shows where they were roughly 52 million years ago, prior to 300 miles of Denali Fault movement.
Sean Regan's photo looking over the Lynn Canal from the northern Coast Mountains in Southeast Alaska on the December cover of Geology.
The massive Pacific Plate colliding into and sliding past Alaska is causing a slow-moving terrane wreck that is pushing Denali and other Alaska Range mountains up to epic heights, enriching the state with minerals, and creating a dynamic tectonic environment that is witnessed by the magnitude seven-plus earthquakes that shake America's Last Frontier every couple of years.
New research by Sean Regan, an associate professor at the University of Alaska Fairbanks (UAF) Geophysical Institute, shows that the tectonic forces at play in southern Alaska broke a geological feature that was whole some 52 million years ago up into three pieces and dispersed them along a 620-mile stretch of the Denali Fault – a break in the Earth's crust between geological terranes that have moved roughly 300 miles over that span.
This arc-shaped continental-scale fault that can be seen from space stretches some 1,200 miles across Alaska and southern Yukon. On the north side of the fault lies the prolific Tintina Gold Belt; on the south side lies the Wrangellia and other mineral-rich geological terranes carried north by the Pacific Plate and piled upon Alaska millions of years ago.
Map shows the epicenter of a magnitude 7.9 earthquake along the Denali Fault in 2002.
The Denali Fault is easily recognizable as an arc that runs through the epicenter of the 2002 Denali Earthquake.
While geologists have been sorting through the terrane wreckage to begin piecing together Alaska's distant past, putting an exact date on when and where the geological features were located millions of years ago has been tricky due to the terranes crashing into each other, breaking apart, being thrust up, pushed down, and transported for hundreds of miles after they collided with the Far North State.
Regan – with help from doctoral student McKenzie Miller, recent master's graduate Sean Marble, research assistant professor Florian Hofmann, and others – has been able to reverse the clock roughly 52 million years to a time when three sites that are now more than 300 miles apart were once a single geological feature located roughly in the area that is now Southeast Alaska.
"Our understanding of lithospheric growth, or plate growth, along the western margin in North America is becoming clearer, and a big part of that is related to reconstruction of strike-slip faults such as the Denali Fault," Regan said. "We're starting to recognize those primary features involved in the stitching, or the suturing, of once-distant land masses to the North American plate."
In addition to the significant academic implications, Regan's work could help economic geologists discover new deposits of precious and critical metals that were formed, jumbled, and transported during the terrane wreck that is Alaska.
Regan's investigation into the terrane wreck focused on geological formation at three locations – the Clearwater Mountains of Southcentral Alaska, the Kluane Lake region of southwestern Yukon, and the Coast Mountains near Juneau, Alaska.
This image reconstructs the Denali Fault based on key markers (red and orange stars). The left image shows the current location of the sites of the Southcentral Alaska and southern Yukon sites sampled by Regan. The right image shows where they were roughly 52 million years ago, prior to 300 miles of Denali Fault movement.
While these now widely dispersed formations are geologically similar, geologists had never determined whether any of them are definitively related to any of the others.
"When you think about geologists crawling around Earth's surface trying to understand what the heck happened, it makes some sense that they might not link things that are so far apart," Regan said of the three sites he studied. "With different geologists working in different areas, the dots don't really get connected until you can reconstruct deformation on the Denali Fault."
With some help from monazite, a mineral enriched with rare earths and other elements, the UAF associate professor was able to prove that the three locations once formed a terminal suture zone. Such suture zones are created when tectonic plates or geological terranes are merged into a larger mass.
"It is just the most special little mineral," he said of the monazite. "It can participate in a lot of reactions, so we can use it as a way to track the mineralogical evolution of a rock."
The suture zone studied by Regan is a geological feature created when the Wrangellia Composite Terrane – a geological island arc enriched with nickel, copper, cobalt, platinum group metals, and other critical minerals – crashed into Alaska and western Canada between 72 million and 56 million years ago.
Regan used inverted metamorphism, a geological phenomenon where rocks formed under higher temperatures and pressures are found overlying rocks formed under lower temperatures and pressures, to stitch together the three sites. Geologists use this reversal of the typical sequence of metamorphism to reconstruct the crustal deformation and mountain building that happens when tectonic plates collide.
With the monazite samples collected from the inverted metamorphic features, Regan discovered several commonalities between these geological features, now spread out over more than 600 miles of Alaska and Yukon, were all part of the same geological unit at the same locale about 52 million years ago.
"We showed that each of these three independent inverted metamorphic belts all formed at the same time under similar conditions," Regan said. "And all occupy a very similar structural setting. Not only are they the same age, they all behaved in a similar fashion. They decrease in age, structurally, downward."
The combination of these unique features adds up to compelling evidence that they were once a suture zone that was torn apart by the Denali Fault and transported across Alaska and the Yukon.
The longstanding collision of distant geological formations into Alaska has enriched the state with a wide variety of minerals and deposit types. Geologists are sifting through the multi-terrane pileup that is now southern Alaska, southwestern Yukon, and northwestern British Columbia to find rich mineral deposits.
"We have got all these mineral deposits and mining districts because the geology of Alaska is composed of rocks of multiple ages, formed by a wide variety of geological processes, arranged in these various terranes that slammed into each other in what is present-day Alaska. Each of the terranes had components like back-arc basins, volcanic arcs, and basins; and each of those components have associated mineral deposits," David Szumigala, a geologist at the Alaska Division of Geological & Geophysical Surveys, explained to North of 60 Mining News in 2010.
At its average rate of movement, the Tintina Gold Belt on the north side of the Denali Fault would have slid roughly five inches to the west over the 14 years since Szumigala talked with Mining News about the geological terranes, and more than 300 miles over the 52 million years since the suture zone studied by Regan was still in one piece.
Regan's ability to locate the time and place of one geological structure in Alaska and Yukon's distant past, and the movements of three separate pieces after it was broken by tectonic forces, provides another piece of evidence geologists can use to sift through the slow-moving terrane wreck as they seek new deposits of the minerals and metals critical to America's economy.
Sean Regan's photo looking over the Lynn Canal from the northern Coast Mountains in Southeast Alaska on the December cover of Geology.
From a mineral exploration perspective, it is interesting that Regan's study connects the area near Alaska Energy Metals Corp.'s Nikolai nickel-copper-cobalt-platinum group metals project in Alaska to an area of southwestern Yukon enriched with the same suite of metals, including Nickel Creek Platinum Corp.'s Nickel Shäw project.
While the evidence is circumstantial, the same geological forces that broke up the suture zone studied by Regan may have also split a critical minerals-enriched block and dispersed it along a 600-mile stretch of the Denali Fault. If so, a clearer picture of what the landscape looked like when the block was a whole could provide geologists with new ideas on where to discover deposits of the nickel-copper-cobalt-platinum group metals increasingly important to clean energy technologies.
Alaska geologist Curt Freeman told Mining News that the dynamic geology caused by the Pacific Plate colliding into Alaska has not only delivered mineral-rich deposits like Nikolai and Nickel Shäw but "also created the exact condition needed to create new ones – heat, fluid motion and faults that allow fluids rich in metals to migrate and coalesce into orebodies."
Geologists sorting through the terrane wreck in search of the orebodies carried north on the Pacific Plate, and the new ones created as it crashes in Alaska now have another bit of evidence to work with, thanks to Regan and his team.
Regan's study was featured on the cover of the December edition of Geology, the journal of The Geological Society of America.
Over his more than 16 years of covering mining and mineral exploration, Shane has become renowned for his ability to report on the sector in a way that is technically sound enough to inform industry insiders while being easy to understand by a wider audience.
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