The international search for a clean, reliable source of energy has cast the spotlight on nuclear power, landing Canada’s Athabasca Basin squarely on the international investment community’s radar screen. Northern Saskatchewan is host to the world’s premier source of uranium with ore grades exceeding 100 times the worldwide average. In a world where uranium is mined at ore grades of 0.2% to 0.4%, the Basin has uranium concentrations ranging from 3% to 26%. As well, growing nuclear programs in developing countries combined with worldwide supply shortages have pushed the price of uranium oxide up from US$10/lb to nearly US$50/lb in just four years, and there’s no end in sight.
As a result, hundreds of new junior exploration companies are back in the Athabasca Basin after a 30-year hiatus, invading the region like ants at a picnic. They have literally staked the Basin from end to end in the race for the world’s next uranium super deposit. Their results vary. So, how does the investor begin to evaluate and identify who’s on target for a find?
THE ANATOMY OF A SUPER DEPOSIT
The Athabasca Basin formed within a bowl or depression in the Canadian Shield, in mining terms referred to as the “basement”. Sand began filling this bowl approximately 1.7 billion years ago and over time became sandstone. It is near the contact point where the sandstone meets the basementthe unconformitythat deposits are formed, hence the term “unconformity deposits”.
By analyzing the known deposits in the Basin we can produce a composite picture not only of the orebody but of its surrounding environment. These specific elements become the clues or indications that one is closing in on the prize.
The first common feature of Basin super deposits is a structural trap, an area where uranium-rich fluids could have pooled and deposited uranium minerals. These traps all have two notable aspects: faulting and graphite. Faults can be created where graphite causes a weakness in the basement rock. The fault provides channels for mineralized fluids to flow and can create a “step” where an uplifted block of basement rock forms a trap by blocking the flow of uranium-rich fluids along the unconformity.
The process of uranium deposition results in another common clue, an alteration halo surrounding the orebody. Alteration is caused by hydrothermal or “hot” fluids passing through a rock and changing its composition by adding or removing minerals. In the Basin, alteration of the sandstone enveloping a uranium orebody can form a halo that is tens to hundreds of metres thick.
There are two clear indications that you are within an alteration halo. The first is the existence of elevated uranium and indicator metals, detected in geochemistry results. The existence of uranium in any common unaltered sandstone sample ranges between 1 and 2 ppm. The outer edge of an alteration halo will have anomalous uranium content of greater than 3 ppm. Closer to the deposit, uranium within the halo will be enriched to more than 10 ppm.
The second attribute of an alteration halo is the presence of alteration minerals or “cooked rock”. At the outer edge of the halo this may be observed as bleaching in the rock while closer to a deposit, that same rock will be more intensely altered to form clay minerals and chlorite.
The unconformity itself provides the most unrestricted path for uranium-rich fluids to flow. During a deposit’s creation, the signature of the fluids at the unconformity can exist well beyond the boundaries of the sandstone alteration halo. This signature will present itself at the unconformity as a very short spike in uranium levels of anywhere from 10 to 300 ppm. Such an indication may not be evidence of a deposit next door, but it certainly means you are in the right neighbourhood.
In summary, explorers must look deeper than elevated uranium at the unconformity as an indication that a super deposit is nearby. There must be evidence that the site is in the vicinity of the alteration halo and that there is a structural trap sitting at a depth that can be extensively drilled. Only when these circumstances are in place, can we say that the site may be a safe bet for the next Athabasca uranium super deposit.
(This article was submitted by PUREPOINT URANIUM GROUP www.Purepoint.com, which is actively exploring the Athabasca Basin.)