High hopes for isotopes

1 of 3Soil sampling is not new in exploration—but Uravan's technique of separating clays from soils was unorthodox and gave a more complete view of the elements present. — Photo courtesy Larry Lahusen

2 of 3Tree coring allowed scientists to chart lead ratios back many years. — Photo courtesy Larry Lahusen

3 of 3An overhead view of the Outer Ring Project in the Athabasca Basin. — Photo courtesy Larry Lahusen

From its beginning, Uravan Minerals Inc. has had a focus on innovation, research and development. Larry Lahusen, the company founder and CEO, has spent much of his life involved in exploration, from uranium in the Colorado Plateau to gold in the 1980s and ‘90s in Canada. He founded Uravan Minerals in 1997, searching first for nickel-copper and platinum group elements on the Rottenstone project in Saskatchewan.

In 2004, the uranium market had recovered sufficiently enough for Uravan to begin hunting for the next high-grade sources of the mineral. They started in the Thelon Basin in Nunavut, searching the Garry Lake project in the northern Thelon and teaming up with Cameco Corporation to explore the Boomerang project in the southwest Thelon. More recently, Uravan has acquired a number of properties in the Athabasca Basin from Cameco, as well as staking two additional claims, the Outer Ring project and Johannsen project properties.

The traditional method of determining uranium drill targets is through geophysics—measuring the electromagnetic (EM) responses of conductors. However, there are challenges with using EM imaging at greater depths, when the resolution of EM conductors decreases. Additionally, though previous drilling in the Athabasca Basin has shown that uranium deposits are found within 25 metres of a conductor, many conductors exist without adjacent deposits. How can explorers narrow down which conductors are drill-worthy?

The answer may lie within geochemistry, specifically lead isotopes.

“We needed to have something else that was going to get us from in the neighbourhood to finding the right house on the block,” said Lahusen. “Geochemistry was the way we went after this.”

Uranium-238 (U238) and uranium-235 (U235) decay to lead-206 (Pb206) and lead-207 (Pb207), respectively. The only source of these lead isotopes is uranium. In vegetation, soils and water removed from uranium deposits, the 207/206 ratio is approximately 0.9—generally known as common lead. At a uranium deposit, the 207/206 ratio is 0.10, referred to as radiogenic lead. As the radiogenic lead isotopes migrate away from the uranium deposit, the resulting mixture of radiogenic and common lead exhibits a 207/206 ratio of less than 0.65.

This anomalous isotope ratio may hold the key to identifying drill targets, but it has taken several years of research to understand the process of isotope migration. Uravan began researching lead isotope ratios at the Boomerang project, sponsoring a PhD student from the Queen’s Facility for Isotope Research (QFIR) at Queen’s University in Kingston, Ontario. Through soil and vegetation samples, as well as analysis of the basin sands, Uravan and QFIR were better able to understand fluid movement and reactivation of basement structures. They also used an unorthodox method of preparing the soil samples, and separated clay from soil, thus analyzing a homogenous sample of clay. This concentrates any of the mobile elements from greater depths.

Next, fellow exploration companies AREVA and Cameco allowed Uravan to conduct a study on the Cigar Lake deposit, a known high-grade uranium source. Soil and vegetation samples were taken; elements present within the fracture zones above the deposit were identified and tree cores were analyzed.

The results, which showed clear isotopic signatures and elements that had migrated through sandstone, were promising—so much so that Uravan and QFIR have entered into a three-year grant to further study the theory behind isotope migration. Uranium deposits—and other mineral deposits such as copper-lead—are, as Lahusen said, “big lunch boxes for microbes.” The microbial activity creates gaseous compounds that travel upward, leaving behind the identifiable elemental and isotopic anomalies.

A current focus at Uravan is drilling on its Outer Ring project. It is here that applied research, employing the results from the Cigar West study, becomes evident, as the drill targets are based solely on geochemistry. Spectral analysis of core samples will be compiled to deduce the hydrothermal activity that has occurred. A weak acid leach of core sand grains—another innovative approach—will shed light on the fluids that have travelled through the sandstone, potentially including radiogenic lead. Though all five holes may not indicate uranium mineralization, positive results would signify that Uravan is looking in the right area.

“This is the first time ever that anyone has drilled a geochemical target without a geophysical signature,” said Lahusen. “If it’s successful, it’ll be a game-changer with regard to how exploration is carried out in the Athabasca Basin.”