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Earth Explorer is an online source of news, expertise and applied knowledge for resource explorers and earth scientists. Sponsored by Geosoft.


News & Views

News Archive

December 7, 2016

Geosoft introduces IP and resistivity inversion in VOXI Earth Modelling

Geosoft has added induced polarization and resistivity data inversion to its VOXI Earth Modelling 3D inversion software service. Geoscientists are now able to create detailed 3D models of conductivity and chargeability from IP and resistivity survey data with VOXI. The resulting models can assist in interpreting and targeting regions for mineral and environmental applications...

December 5, 2016

Mexico's Deepwater Round Exceeds Expectations

Some of the world's biggest oil companies showed up Dec. 5 and agreed to invest on the Mexican side of the Gulf of Mexico, proving that deepwater exploration still has a pulse despite challenging market conditions...

November 30, 2016

Magnetic inversion results for Ngamiland available for download

A regional-scale geophysical inversion of magnetic field data in the Ngamiland region of northwestern Botswana is now available for download from the Botswana Geoscience Portal, a partnership initiative of the Botswana Geoscience Institute, industry sponsors and Geosoft...

November 30, 2016

LIGO Resumes Search for Gravitational Waves

After a series of upgrades, the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory, have turned back on and resumed their search for ripples in the fabric of space and time known as gravitational waves. LIGO transitioned from their engineering test runs to full science observations at 8 a.m. Pacific Standard Time on November 30...

November 9, 2016

International Volcano Scientists Unite

For the first time, the United States will host the international Volcano Observatory Best Practices workshop, previously held only in Italy. The workshop will take place this month in Vancouver, Washington. It is designed specifically for volcano observatories around the world and their staff to exchange ideas and best practices with each other...

October 4, 2016

USGS Assesses Mineral Potential for Sagebrush Habitats in Six Western States

USGS has completed a comprehensive assessment and inventory of potential mineral resources covering approximately 10 million acres of Federal and adjacent lands in Idaho, Montana, Nevada, Oregon, Utah and Wyoming...

October 3, 2016

Uganda Targets Up to U.S.$100 Million for Mineral Exploration

Uganda is well endowed with mineral resources and, like many naturally-gifted African countries, is becoming keen on ensuring that these resources play a transformative role in its long-term structural transformation dream - the Vision 2040...

September 9, 2016

Small-Scale Fishers Get A Big Boost With First-Of-Its Kind Impact Investment Fund

Conservation organization Rare announces the Meloy Fund for Small-Scale Fisheries at Our Ocean Conference. The Global Environment Facility, one of the largest funders of conservation worldwide, will be investing $6 million into the fund...

September 1, 2016

Scientists take to the skies to track West African pollution

Scientists operating research aircraft over West Africa have detected organic materials in the atmosphere over a number of urban areas, contributing to concerns of the rise in pollution across the region...

August 17, 2016

New IGS Xplore prospectivity maps for Botswana

International Geoscience Services have released a series of base metal prospectivity maps for the Ngamiland District of northwestern Botswana using free geodata available on the recently-launched Botswana Geoscience Portal, hosted by Geosoft. The maps identify favorable areas for copper, zinc and lead mineralization using geological, geochemical and geophysical datasets downloaded directly from the portal.

August 11, 2016

NexGen Makes New High Grade Discovery

NexGen Energy reported the discovery of a new high grade zone of mineralization 4.7 km northeast of the Arrow Deposit as part of an on-going summer drilling program on its 100% owned, Rook I property, Athabasca Basin, Saskatchewan...

August 10, 2016

Rampion UXO Disposal to Take Place This Week

E.ON has confirmed that the two unexploded devices, detected along the Rampion offshore cable route will be safely disposed this week following the consultation with the Marine Management Organisation...

August 9, 2016

Diamonds In The Rough: E&Ps Find New Reserves In Mature Basins

The oil industry’s history demonstrates clearly that new plays and prospects have long been found in mature basins that were thought to be well on the way to being squeezed dry. Through the acquisition of new data, developing new concepts and coming up with fresh interpretations, long-producing basins around the world from the North Sea to Malaysia have continued to reveal new riches...

August 8, 2016

Northern Shield Identifies High Quality VTEM Targets at Séquoi

Northern Shield Resources announced the results of the interpretation and modelling of the VTEM survey from the Séquoi Property in the Labrador Trough of Quebec . Séquoi is owned 100% by Northern Shield and is being explored for Noril'sk style Ni-Cu-PGE massive sulphides. After geophysical modelling and interpretation of the VTEM data from Séquoi, six VTEM anomalies of significant interest have been identified...

August 3, 2016

Rio Tinto tailors big data drive to copper

Rio Tinto will put the weight of an exploration big data push and its newly-formed Growth and Innovation group behind its desire to identify a "tier 1" copper asset. Speaking at the annual Diggers & Dealers conference in Kalgoorlie, Growth and Innovation group executive Stephen McIntosh said Australia was "overdue for a tier 1" mineral discovery of any type...

August 1, 2016

Tetra Tech Awarded $200 Million Navy CLEAN Contract

Tetra Tech announced that it has been awarded a $200 million, single-award contract by Naval Facilities Engineering Command (NAVFAC) Atlantic. Through the Comprehensive Long-term Environmental Action Navy (CLEAN) contract, Tetra Tech will provide environmental engineering support services to installations within the NAVFAC Atlantic Area of Responsibility...

May 3, 2016

NATO Science for Peace and Security (SPS), MODUM Partners announce "Young Scientist Summer School on Sea Dumped Chemical Weapons"

This international project cooperates closely with CHEMSEA (Search and Assessment of Chemical Weapons) Project for and sharing and knowledge transfer...

April 12, 2016

Monday mad rush for gold stocks

Renewed optimism about the outlook for gold saw investors pile back into gold stocks, pushing many stock to 52-week highs in heavy volumes...

April 11, 2016

Medgold Resources: Continues to Expand the Boticas Gold Project, Portugal; Proposes $200,000 Private Placement

Medgold Resources is pleased to announce new assay results from contiguous rock-chip sampling from the Limarinho South zone at its Boticas gold project in Portugal, which include a highlight of 6.0m @ 5.7 g/t Au...

April 8, 2016

De-carbonizing our energy sector

Nuclear energy currently provides around 11 percent of the world's electricity. China, the European Union, the United States, India, Russia, South Korea, and other nations’ have major existing fleets...

April 1, 2016

Follow-Up Drilling Results Indicate Wide Gold Zones at Hendricks Gold Discovery

Gascoyne Resources Limited announced that it has received the final assay results from the 10,000 metre aircore exploration drilling programme...

March 26, 2016

The Oil Market Is Finally Hitting Its Breaking Point

After a significant reduction in investments over the past two years, oil companies can no longer overcome the production declines from legacy wells...

March 15, 2016

N-Sea Expands into the French Offshore Wind Industry

Subsea IMR provider, N-Sea, has signed a letter of intent with CERES Recherches & Expertise Sous-Marine and TechSub Industrie Environement, to provide subsea survey, installation and remediation services to the French offshore wind industry...

March 9, 2016

PDAC 2016 Convention Exceeds 22,000 Attendees

Optimism and opportunity abounded at the PDAC 2016 Convention of The Prospectors & Developers Association of Canada in spite of recent industry challenges...

March 3, 2016

6 Alpha Launches EOD Contracting Division

6 Alpha Associates, a specialist risk consultancy practice, with expertise in the assessment and management of unexploded ordnance, has launched a dedicated explosive ordnance disposal division...

Uranium Exploration: A Guide for the Uninitiated


Virginia Heffernan



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 resources.

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 plutonic rocks.

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 shallowest.

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

Exploration techniques currently being used in the basin are outlined below:

Area Selection.
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 conductors.

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.

Geochemical Sampling
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 deposits.

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 alteration.

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.

Ground Geophysics
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.

Drilling
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.

Data Management

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.”

References:
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, p126-138.

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 and Resources.