ESO Uranium digs into the Athabasca Basin

Ben Ainsworth joined the board of Hathor Exploration in 2005 and served as vice president exploration during the junior’s development of its high-grade Roughrider uranium deposit in northern Saskatchewan’s Athabasca Basin, about 25 km from Cameco Corp.’s (CCO-T, CCJ-N) mill at Rabbit Lake. Late last year Rio Tinto (RTP-N, RIO-L) outbid Cameco Corp. in a successful $642 million takeover bid for the junior uranium explorer. 

Today Ainsworth is back at it again as vice president exploration of another promising junior uranium exploration company, ESO Uranium Corp. (ESO-V), which is investigating high-grade targets on its Patterson Lake South property in a 50-50 joint venture with Fission Energy (FIS-V).

“Patterson Lake South is a very exciting project,” says the Oxford University trained geologist, who counts among his career highlights the 1972 discovery of Howards Pass, a massive zinc/lead deposit that straddles the border between the Yukon and the Northwest Territories and which is currently being developed by Selwyn Resources (SWN-V), and the 1995 discovery of the first reported marine alluvial diamonds off Sierra Leone. Ainsworth was also involved in the development of the copper-molybdenum Huckleberry open pit mine in British Columbia, which is currently owned by Imperial Metals (III-T) and a Japanese consortium of Mitsubishi Materials Corp., Marubeni Corp., Furukawa Co. and Dowa Mining.

The excitement about Patterson Lake dates back to June 2011 when Ainsworth’s son Garrett, also a geologist, discovered a field of high-grade uranium boulders on the property, about 80 km south of the former Cluff Lake uranium deposits that together produced more than 60 million pounds of U308 before being shut down about a decade ago. The property also lies about 50 km to the south of the Shea Creek deposit owned by UEX Corp. (UEX-T) and Areva.

“It’s probably one of the biggest boulder field discoveries in the Athabasca Basin,” Ainsworth says in an interview. “And they are unusually large and high-grade for that part of the world…we expect that somewhere on the property we’ll find mineralization that could have been scoured off by the ice and moved over to where the boulder field is.”

So far ESO and joint-venture partner Fission Energy have traced the boulder field in a north-south direction for a distance of about 5 km and to widths of up to 1 km.

The substantial size of many of the well-mineralized boulders seems to indicate that the travel distance from source could be comparable to the distance between Patterson Lake and some of the deposits that made up the Cluff Lake mine.  Patterson Lake South is accessible by road from Highway 955, which runs to Cluff Lake and passes near Shea Creek.  

“We have some indication from looking at assessment reports of the Cluff Lake mine area that it’s not uncommon to find boulders in patches that are down-ice from what are now some of the old pits of the Cluff Lake mine operation, 2-3 km away,” Ainsworth says.  

Last year ESO Uranium reported that twenty-five of the boulders had grades of more than 10% U308 with the highest grade assaying 39.6%. The largest boulder—measuring greater than 40 cm at its longest dimension from a partially recovered block at a depth of 90 cm—assayed 25.7% U308. Twenty-three other boulders on the property assayed between 1.0% U308 to 10% U308.

At the start of 2012, ESO and Fission launched a $2.76 million 33-hole winter drill program that will include sonic and reverse circulation drilling, core drilling and airborne and ground geophysics with the goal of locating the bedrock source of the high-grade boulders.

Highlights from drilling released earlier this month include hole 12-013, which returned a basement intercept of 19 metres averaging 935 counts per second (cps) starting at a shallow depth of 98.17 metres from surface, including 7 metres averaging above 1000 cps. (Counts per second are due to gamma radiation measured by a borehole probe.)

On Apr. 24, the company reported results from three more holes with elevated radioactivity. Drill holes PLS12-014 to 016 all intersected strongly anomalous gamma radiation values based on down-hole gamma logging and hand-held scintillometer analysis.

Drill hole PLS12-016 had the best average radioactivity, which averaged 2516 cps over 4.45 meters with a maximum value of 6032 cps. Hole PLS12-015 had 1.95 metres of 662 cps in Mesozoic clastic sediments at 94.59 metres, and hole PLS12-016 had 0.25 metres of 710 cps in Devonian clastics at 54.96 metres.

Ainsworth believes that the composition of the rock types in the boulder train suggest that the mineralization may be a basement-hosted system in an area where the Athabasca sedimentary rocks have been scraped away by ice action and the depth to the basement is expected to be less than 100 metres in the project area.

And he expects to find a high-grade, Shea Creek-type deposit, in the basement rocks. “Shea Creek is the nearest deposit to us and has got high-grade mineralization in the Athabasca sandstone above its basal unconformity with the Archaean basement rocks,” he says. “But the mineralization also occurs in significant amounts down into the basement and it’s on a 3-km-long structure.” Shea Creek also has a bit of gold in it, as Cluff Lake did, and as the Patterson Lake boulders do, he notes.

“It can’t be too far from the source because we know the Athabasca sandstone is covering basement rocks to the northeast, not far from the northeastern edge of our claim block,” Ainsworth says.

“Fortunately we anticipate the source will initially be quite shallow. The overburden cover varies from something around 55 metres in Patterson Lake itself to a little bit less than 100 metres on land.”

In addition to its Patterson Lake South project, ESO Uranium has three other projects in the Athabasca Basin: Cluff Lake, Hook Lake and Cree.

One Cluff Lake project adjoins the former Cluff Lake mining lease open-pit mine and the Shea Creek project and is a 50-50 joint venture with Rio Tinto, a result of the major’s takeover of Hathor Exploration last year.

The second Cluff project is a claim block on the east side of the same mining lease, which also has targets that were identified by the earlier work of Amok (Areva’s  predecessor), which found boulders down ice along the boundary of the mining lease.  

At presstime in Toronto ESO Uranium was trading at 8.5¢ per share within a 52-week range of 4.5¢-14.5¢. The junior has about 130 million shares outstanding.