State Completes New Magnetic Surveys of Historic Mining Area

Sample map from recent aerial research. (Source: Alaska DNR -DGGS)

Southwest Alaska has a special place in the state’s mining history with the gold rushes in the Iditarod and Aniak areas. It’s also where the future of gold is happening, at the nearby Donlin Creek project. The area now is getting a fresh look with the most recent survey technology.

The state has recently finished an extensive geological survey of historic mining areas near the Aniak, Innoko, and Iditarod mining districts. Steve Masterman is the division operations manager with division of Geological and Geophysical Surveys. He says one of the agency’s goals is to evaluate state lands for metal and mineral potential.

”As part of that mission, we go out and look at areas that are heavily mineralized, have lots of know or past mineral production or known mineral occurrences and we collect this kind of information to help people locate more mineral resources in those areas,” Masterman said.

This is an area with a strong history of gold production. Since 1880, Miners have produced more than 2.8 million ounces of gold, most of it placer gold. The state thinks there is more to be found in igneous rocks. Much of the area has not been thoroughly explored, although the well-researched Donlin deposit is in the area.

The aeromagnetic surveys are done with helicopter that flies lines about ¼ mile apart. They’re sending out signals that bounce back and measure the magnetic response of the rocks and their resistance to electricity.

“If a rock is very conductive, it can be conductive because it has a lot of clay, or carbon, or if it has a lot of metals. So you can trace different beds of rock or different rock formations,” Masterman said.

Masterman says a preliminary look at the maps show shows more faulting and folds of rock formations that can give a can better understanding of how the geology works.

“We can also see more intrusive and volcanic rocks, and it’s the intrusive and volcanic rocks associated with gold mineralization at Donlin Creek and Nixon Fork and other places in that part of the world, so that’s also good to see,” Masterman said.

The surveys cost about a million dollars.

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Ben Matheson is a contributor with the Alaska Public Radio Network.