Geologists seek to resolve differences between Yukon and Alaska maps

Alaska Dispatch News

ANCHORAGE — Alaska-Miners were pulling gold out of eastern Alaska even before the thousands of fortune hunters rushed north to the Klondike gold fields next door in Canada’s Yukon Territory.

But more than a century later, no one is entirely sure of the precise geologic source of gold in the Ladue River unit, which includes Alaska’s historic Fortymile mining district, among others.

While maps of Canada’s Klondike region just to the east are up-to-date and precise, thanks to periodic fine-tuning with new surveys and modern technology, geologic maps for the Alaska area right across the border are less detailed and do not match the Canadian side.

The U.S. Geological Survey, with help from counterparts in Canada, is trying to address that discrepancy.

Jamey Jones, of the USGS’s Alaska Science Center, has been leading a team of geologists making summer treks to the area to look at the rocks protruding above ground to better understand the bedrock below.

The Canadian maps provide details of what is known as Klondike schist, the formation that is believed to have provided the gold that triggered the history-shaping Klondike Gold Rush at the end of the 19th century. That type of rock — light-colored, crumbly looking, flecked with a type of flaky mica known as muscovite and also sometimes dotted with bits of red or brown crystal pyrite — “really has a very distinct look,” Jones said.

On the Yukon side, it is well-exposed and well-mapped. But information about the Klondike formation is vague in the Alaska-side maps, which were released in the 1970s.

“It was mapped in eastern Alaska, with a question mark,” Jones said.

The Alaska maps are based on the work done by pioneering geologist Helen Foster. Now 94, Foster was one of few women geologists of her era. She became famous for her work mapping Japan’s geology after World War II. She turned her attention to Alaska later and became a legend in the far-northern geologic world.

“Helen was old school,” said USGS geologist Frederic Wilson, who was an assistant on her Alaska surveys. “She hiked every ridge.” He did not complain, he said.

“Back then, I was young and I wasn’t going to let an older woman outclimb me,” said Wilson, who also worked as an aide to Foster’s colleague, Florence Weber, another pioneering geologist.

Despite their determination, however, Foster and her crew couldn’t get to all the places that needed mapping.

“Helen was as thorough as she could be, given that she only had a certain amount of time to be out there,” Wilson said.

Foster’s mapping identifies some sites as Klondike, but with a question mark, Jones said. Those are sites where she might have seen rock outcroppings from a distance, perhaps from an airplane, he said.

More uncertainty comes from Alaska geological updates, which classify some of what Foster called possible Klondike schist as other types of rock, or mixtures of various rock types.

The new Alaska mapping initiative is focused on sorting out the true identities of those formations, Jones said. His team, totaling six geologists, has been retracing Foster’s steps and studies.

In the summer of 2013, the team investigated road-accessible rock formations. Last summer the geologists traveled by helicopter to more remote sites. More surveys are planned for next summer.

The on-the-ground surveys led by Jones have, so far, found that some outcroppings do indeed look like Klondike schist, but that others appear to be something different. In general, while there is some Klondike formation that extends into Alaska, the vast majority is on the Yukon side, he said.

Jones said he and his colleagues hope to have their findings published by next year, and to see Alaska and Yukon digital geologic maps updated after that.

Compared with the Canadian mapping effort, the Alaska work is a bare-bones effort, as Jones describes it. The annual budget, above normal salaries, has been about $55,000, covering expenses of helicopter flights and other necessities. The Canadians, in contrast, spent about 10 times that much do their Yukon mapping work, Jones said. The Canadian work is conducted by the Yukon Geological Survey and the federal counterpart to the USGS, the Geological Survey of Canada.