Uranium Exploration: A Guide for the Uninitiated
A drill rig exploring in the Shea Creek area south of AREVA’s former Cluff Lake mine site. Photo courtesy of AREVA Resources Canada.
A six-fold increase in the uranium price to more than US$60 per pound over the past three years has sparked a worldwide uranium rush. There are now an estimated 400-plus companies looking for new resources or reviving old plays that were abandoned when declining uranium prices stifled exploration in the 1980s.
The problem is, hardly anyone knows how to explore for uranium. There has been so little interest in the radioactive metal over the past few decades that a whole generation of exploration geologists has grown up without ever handling a scintillometer. The experts in the field are mostly retirement age or older.
Take Bob O’Dell, for instance. “They dug me up and put me to work,” the 80-year-old geologist told The Economist after being hired by Energy Metals, a Canadian uranium explorer, to consult on the company’s exploration projects in the U.S.
Younger geologists have a steep learning curve ahead. With that in mind, we provide a summary of the latest exploration techniques in the uranium patch.
Focus on unconformity-related deposits
The summary focuses on unconformity-related deposits, the most common
of the 14 major categories of uranium deposit types. These deposits
provide all of the uranium production from Canada, the world’s
largest uranium producer, and comprise a major proportion of Australia’s
In the Athabasca Basin of northern Saskatchewan, the locus of current
production and exploration, unconformity-related deposits are associated
with quartz sandstones and conglomerates filling an oval-shaped basin
that is about 1.5 km deep at its centre. The sedimentary rocks lie
uncomformably over a basement of metasedimentary, metavolcanic and
Uranium deposits in the basin occur below, within and slightly above
the unconformity and are associated with graphitic zones and major
structures in the Archean basement. They tend to be extremely high-grade
(more than 10% U3O8), but small, deep and difficult to find.
During the first wave of exploration in Athabasca, which was mostly
surface-based, only about 20% of known uranium resources were uncovered.
Finding the rest required advances in deep-penetrating geophysics
and geological models. Even so, most of the finds were concentrated
on the eastern rim of the basin, where the unconformity is at its
Now, exploration is spreading throughout the 100,000-sq-km basin as
a result of more sophisticated technology, even better geological
understanding, higher uranium prices and recent exploration success
in areas previously thought to have limited prospectivity. Uranium
exploration expenditures in the province are expected to exceed $100
million in 2006 compared with $13 million just three years ago, according
to Saskatchewan Industry and Resources.
Exploration techniques currently being used in the basin are outlined
Airborne geophysics has evolved to allow deeper imaging, opening up
areas of the basin that could not be penetrated during previous waves
of exploration. Modern techniques can detect targets under almost
one kilometer of sandstone cover, a depth that would have been inconceivable
just a few years ago. The resolution of airborne data has also improved
– approaching or exceeding that of ground surveys – allowing
direct drilling from airborne results.
High-resolution magnetic and electromagnetic (EM) surveys can detect
basement features where they coincide with graphitic zones, the major
marker for uranium deposits. For example, combined airborne GEOTEM
electromagnetic and magnetic surveys over the Shea Creek area on the
western rim of the basin identified several conductive zones at depths
of 700 metres and greater that were successfully followed up with
ground geophysics and drilling. A variation on GEOTEM, called MegaTEM,
has approximately twice the output power and can detect even deeper
High-resolution gravity (e.g. FALCON by BHP) can also identify favourable
structural features in conductive zones, and seismic surveys are being
used to image the unconformity and related structural features.
Fugro is working on a new EM system called Tempest that has better resistivity resolution than GEOTEM and is expected to be well-suited for mapping zones of moderate resistivity with the sandstone that may indicate alteration.
After a prospective geological setting has been identified using geophysics
to outline faulting and favourable lithologies, the area can be sampled
using geochemistry on a reconnaissance scale. The background geochemical
composition of the Athabasca Basin is low, so even subtle enrichments
of key elements can be detected. The suite of pathfinder minerals
includes U, B, Pb, Ni, Cu, As, Co, Mo, Zn, V and the rare earth elements.
However, the use of geochemistry is limited by the fact that unconformity-related
deposits have a small footprint and usually occur at significant depths.
The Athabasca area has less than 1% outcrop exposure and is covered
by a layer of glacial drift up to 100 metres deep.
Because glacial overburden is so predominant, sandstone boulder sampling
has evolved to detect distinct geochemical signatures, or alteration
halos, associated with uranium mineralization. Studies of hydrothermal
alteration around uranium deposits shows that these halos can extend
upward into subcrop, sometimes through hundreds of metres of sandstone
and, by extension, into the glacial till that overlies the uranium
As a result, boulder sampling has emerged as an effective means of
finding alteration halos since lithogeochemical anomalies found in
the boulders are almost as strong as those found in the subcrop, according
to a paper on glacier boulder lithogeochemistry published in the proceedings
of a symposium held in Regina in November 1989 (see references). Even
when the signature is weak, improved analytical techniques with lower
detection limits for uranium, boron and lead can be used to detect
According to Ken Wasyliuk of JNR Resources, a composite of sandstone
boulders consisting of 5–10 of the largest, most angular boulders
available at each sample station should be collected at regularly
spaced intervals. The source of the anomalous boulders can then be
traced back to the subcrop. The relative speed and economy of boulder
sampling compared with other exploration methods make it a popular
choice for defining the limits of alteration halos.
Drill core can also be sampled using a collection of 1–4 cm
wafers at the end of each row in a core box and compositing them over
a regular interval of 10 metres or so. This way, the average geochemical
values for specific elements can be compared on a hole-to-hole basis
to pinpoint areas of alteration.
Wasyliuk says the future of geochemical exploration in the Athabasca
Basin lies in the development of surface sampling techniques that
can detect mineralization directly. He adds that the programs will
only be effective if combined with consistent sampling, analytical
and QA/QC procedures, as well as adequate documentation and a better
understanding of element movement and distribution in the near surface.
Whereas ground EM surveys were once used routinely to follow-up airborne
surveys with deeper penetration through the sandstone, they are now
more often used to provide detailed assessments of targets of interest.
Time domain systems such as the Crone, Geonics and UTEM EM systems
are the most popular, while frequency domain systems such as Zonge
and Phoenix are also in use. Both types are capable of deep penetration
under conductive cover.
At Shea Creek, UTEM III moving loop array surveys identified a strong
conductor. The subsequent drill hole in 1992, the third of the project,
intersected a uranium-bearing shear zone at a depth of 705 m with
a grade of 0.62% U3O8 over 0.7 m. Follow-up moving loop array surveys
were instrumental in extending the conductor to more than 30 km and
selecting drill targets. The Shea Creek’s Anne deposit is currently
estimated to contain 47 million lbs. U3O8 at an average grade of 3%
U3O8 and remains open-ended, while drilling continues to find new
zones of mineralization.
New developments include array style EM systems such as Quantec’s
Titan that are much more advanced in terms of data acquisition and
subsequent processing. For instance, Titan can acquire magnetotelluric
(MT) and induced polarization (IP) data concurrently, reducing acquisition
costs on a per station basis.
After targets have been identified by a combination of favourable
geophysical and geochemical results, the next stage of exploration
is core drilling. Targets are drilled until a deposit is located or
the anomaly has been explained. Most of the alteration halos in the
Athabasca Basin are, in fact, barren.
One of the most significant changes in technique as exploration pushes
deeper into the basin is the use of directional drilling. Pioneered
by Cogema at the Shea Creek deposit, the technique allows several
intersections to be made from a single pilot hole, reducing drilling
costs and improving target precision considerably. Core orientation
methods are also used at Shea Creek and other exploration projects
to better understand the geology and structural controls on mineralization.
Exploring for uranium requires more data collection from drill core
than any other commodity because the alteration halos around deposits
can be so extensive, even if the target mineralization is elusive.
Geoscientists must collect and interpret reams of structural, stratigraphic,
petrographic, chemical, and spectral data from the core in order to
determine if further exploration is warranted. This requires a sophisticated
data management system.
“Most drill jobs have two geologists and a geotechnician, and the downstream work in managing and interpreting the data has to be within a software environment that is easy to use and flexible from project to project,” says William Kerr, vice-president of exploration and development for Denison Mines Corp., who uses Geosoft’s Target™ to simplify borehole data processing. “We use Geosoft to plot our compiled data at various scales for interpretation and presentation by the geologists.”
Glacial boulder lithogeochemistry: An effective new
uranium exploration technique in the Athabasca Basin, Saskatchewan;
S. Earle, B. McGill, and J. Murphy, p94-114 from Modern Exploration
Techniques; Proceedings of a Symposium Held in Regina, November 20
and 21, 1989: Saskatchewan Geological Society Special Publication
No.10 Edited by L.S. Beck and C.T. Harper (1990).
MinExpo ’96 Symposium – Advances in Saskatchewan Geology
and Mineral Exploration; Edited by K.E. Ashton and C.T. Harper; Saskatchewan
Geological Society Special Publication No.14, Proceedings of a symposium
held in Saskatoon November 21 and 22, 1996 (1999): Shea Creek –
A Deep Geophysical Exploration Discovery; Rodney R. Koch and Frank
Dalidowicz, p96-108 & Advances in the Genetic Model and Exploration
Techniques for Unconformity-type Uranium Deposits in the Athabasca
Basin: K. Wheatley, J. Murphy, M. Leppin, C. Cutts, and J.A. Climie,
2006 CIM Uranium Field Conference: Athabasca Basin & Analogues:
Geochemical methods in the Athabasca Basin – Past, present,
and future. Ken Wasyliuk (JNR Resources Inc.). The author would also
like to thank David MacDougall and Colin Card of Saskatchewan Industry