The people, science and technology behind discovery

A formula for higher hit rates? NexGen may have it

by Virginia Heffernan on May 14, 2015 applied

The methodical, collaborative way the technical team goes about exploration has provided the backdrop for NexGen’s extraordinary hit rate on the Arrow zone of the Rook I property. Shown above: NexGen VP of Exploration Garrett Ainsworth.

NexGen Geologist Justin LaFosse spotting drill collars.

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Rook 1 drilling, Arrow property, Feb 23 2105

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Fury target areas: EM conductors with gravity background.

As exploration moves deeper into the subsurface, achieving a high hit rate is becoming increasingly difficult. Without outcrop or other surface geochemistry to guide the way, explorers are drilling almost blind, relying on sometimes nebulous geophysical signatures to find hidden targets.

Yet by combining geological insight, tailored exploration techniques and comprehensive data compilation, NexGen Energy has hit the buried Arrow zone on the Rook I property that straddles the southwest margin of Saskatchewan’s Athabasca basin in almost every hole.

Rook I abuts Fission Uranium’s Patterson Lake South (PLS) project, which hosts the Triple R deposit, considered one the best grassroots mineral discoveries of this decade. Two years ago, NexGen drilled what looked like a northeastern extension of a PLS EM conductor and intersected strong hematite and clay alteration and sniffs of uranium mineralization at Area A.

A follow up campaign on the Rook I property discovered the Arrow zone in the first hole, and subsequent drilling delineated high grade mineralization over a strike length of 515 m and a width of 215 m in 40 of 42 holes.

Arrow remains open along strike as NexGen continues an 18,000 m winter program with three rigs, stepping out from the original discovery and hitting the stacked sub-vertical mineralized shear zones that represent Arrow with impressive regularity.

In March, NexGen announced the widest high grade intercept the basement gneisses to date: 70 metres grading 2.2% U3O8 from 522 metres down hole AR-15-34b, a 30 m step out from the centre of one of the main mineralized shear zones at Arrow.

How do they do it? To be fair, NexGen has an advantage over most explorers in the region because Arrow – like the neighbouring Triple R deposit - is shaping up to be a relatively large uranium deposit: a knitting needle among sewing needles in the basin’s haystack. And the mineralization is shallow, ranging in depth from 100-820 m compared with greater than 500 m elsewhere in the basin.

The other benefit the company has is experience: VP of Exploration Garrett Ainsworth was the project manager at PLS from 2007-2013; director Andrew Browne, head of the technical advisory, has been involved in uranium exploration since 1969, working in the Athabasca basin since 1988; and director Craig Perry has lead several exploration programs for Rio Tinto and others.

But the methodical, collaborative way the technical team goes about exploration has provided the backdrop for NexGen’s extraordinary hit rate. “It’s a bit like doing a forensic study,” says Ainsworth, who won the Colin Spence award for excellence in global mineral exploration for his efforts at PLS. “The key is to obtain as many layers of data as possible. Then each layer is given a different weighting to prioritize targets. The highest priority weighting, for example, would go to a historical drill hole with good geology, alteration, structure and radioactivity that has not yet been followed up.”

Because the area is so heavily glaciated, the lowest priority weightings usually go to geochemical anomalies most likely explained by bedrock anomalies up-ice, not in-situ mineralization. The exception is radon gas sampling which, although prone to false negative and positive anomalies depending on environmental conditions, is proving to be an effective tool for detecting the shallower uranium mineralization of the southwestern basin such as at PLS and Rook I.

The type of data collected and the way that data is integrated contributes to the drilling success. With a huge swath of ground to cover, NexGen pores through large volumes of historical data from Saskatchewan’s assessment files, importing digital files and manually entering data from paper files into Geosoft Target while georeferencing everything for accuracy. “It’s quite a process, but when you compare the cost of doing that to the cost of redoing the survey, it’s dirt cheap,” says Ainsworth.

Depending on what the historical data reveals, NexGen runs airborne surveys including VTEM, magnetometer, gravity and radiometrics, then integrates the results of those surveys with the historical compilation to narrow down the area of interest.

The company follows up favourable airborne targets with ground geophysics such as TDEM, ground gravity, and DC resistivity, and where applicable, radon gas sampling. Airborne radiometric anomalies are checked by prospecting with handheld scintillometers, and - if uraniferous boulders are found - trenching and glacial studies to determine which way the boulders travelled and their up-ice bedrock source.

All the while, the team is entering new data into Target in order to zero in on the best drill targets. “Target allows us to do comprehensive compilations by tying in historical data with airborne and ground geophysics and our latest geochemical and drill hole data,” says Ainsworth.  “It graphically communicates important information to both investors and geologists. Being able to communicate with two such different groups with one program is invaluable.”

And with every drill hole comes a better sense of the structural controls on the mineralization, a factor Ainsworth says is key to determining where the next “blow out” of uranium will be.

Once the technical team has had time to digest the results of the current winter drill program, NexGen will launch another 18,000 m program to continue advancing Arrow. The company will also test the Fury area on a different conductor corridor 13.5 km southeast of Arrow, where the team has identified six drill targets based on the results of VTEM, ground gravity and magnetics.

Since Rook I has the potential to host three different types of uranium mineralization, Ainsworth expects exploration to continue indefinitely. “The property straddles the present day edge of the Athabasca basin, which is where you want to be to find shallow high grade uranium, not only within basement rocks but also at the unconformity and within the Athabasca sandstone.”

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