Wheeler River- "Beware of the Darcy's"

I am going to keep this short and sweet.  I never seem to upset CEO’s in the zinc space but it is another matter in the U space.  But hey, I’m on a roll. This internet thing means it is no longer easy to control the flow of information.  Sell side analysts usually keep their mouths shut and buy side analysts are all monks or hermits. So it is awfully tough at times to get some quality information.

Anytime I hear the word “Darcy”  I immediately flashback to the outback of Australia sitting in a Toyota Landcruiser with Herman Radmuller.  We were driving from the McArthur River zinc mine site in the Northern Territory to the Heartbreak Hotel on a Friday night for a few beers at the pub.  Herman said, “Beware of the Darcy’s”. The Darcy family were the local station owners (Malapunyah Station) and the sons loved to go to the pub on Friday nights to pick fights.  The Darcy’s were the J.R.Ewing family of Australia’s Deep North. We kept our backs to the wall while overhearing these guys speak pigeon English/Aboriginal gibberish and exited intact but it was an adventure I have not forgotten.

The term Darcy as it relates to uranium extraction however, is entirely related to the in-situ leaching method.  It is a term borrowed from the oil patch. It measures the ability of fluids to move through rock.

A good primer on ISL mining can be found here:

The Darcy formula details can be found here:

As noted, “Typical values of permeability range as high as 100,000 darcys for gravel, to less than 0.01 microdarcy for granite. Sand has a permeability of approximately 1 darcy.”

One reason some in-situ leach operations are more successful than others relates to this measure of permeability.  Other reasons include, the presence, or lack of confinement and the chemical reaction that occurs to allow the uranium in solid form to dissolve into solution form.  I won’t discuss the later two reasons, although in the case of Wheeler River, confinement is also of great importance. (You can exhale Greg).

So permeability is a critical piece of information but it is seldom provided by the owner of an ISL mine or proponent of a potential ISL operation.   You should ask for it if you are considering an investment in an ISL property. The percentage porosity is also an important factor. In other words, if the leach solution cannot come in contact with the uranium, it will not be recovered.

ISL is technically (though not necessarily commercially) successful if the Darcy values are greater than “a few hundred millidarcies”1 which likely represents a tight or silty sand or sandstone.

So now lets blast forward to the recent NI 43-101 for the Phoenix Deposit at Wheeler River which proposes using ISL for an unconformity related deposit.   Those familiar with unconformity style deposits on the east side of the province know that they are a bit of a dog's breakfast.

McArthur River contains zones of massive or stringer pitchblende in a matrix of fractured sandstone, clay, sand and groundwater.  In this case the sandstone has been silicified leading to low permeability for the individual shards. Fluid flow is fracture controlled.  It is not uncommon to drill an intersection of 5-10 metres of near massive pitchblende with perhaps only a fracture every 0.2 m or so. But it can then be surrounded by an incompetent mess.

In Cigar Lakes’ case the mineralization consists of massive pitchblende nodules in a clay rich matrix.  The nodules I have seen in photos are somewhat like shot puts.

In both cases, the uranium content of both orebodies is heavily weighted to the zones of massive or near massive pitchblende and not the surrounding matrix.

When I read the geologic description for Wheeler River it reminds me more of McArthur River but without the silicification.  It’s geometry though is very much like Cigar Lake. The following table was provided in the NI 43-101 for Darcy values:

The Darcy values are well below the range necessary for successful ISL elsewhere but they are also acknowledged to be unrepresentative.

So the concern I have is this:  I struggle to envision how the leach solution is going to come in contact with much of the uranium present to allow its extraction.  In locations, fluid flow could be fracture controlled meaning the solution may bee line it from an injection well to a production well if a connection between the two can be established in the first place.  I struggle to see how the leach solution is going to get at the heart of massive pitchblende areas in particular. In my mind, good results in the lab were the result of using small diameter de-stressed drill core as the test sample.  What does the ore look like in-situ? The economics rely upon obtaining high recovery (85% was used in the PFS).

I keep picturing in my mind a stream with some boulders in it.  In this case the boulders are pitchblende, The water (leach solution) flows around the boulders (pitchblende) leaving them relatively intact.  So a lot is riding on this pitchblende being extremely incompetent and porous in-situ at Phoenix such that it can then come in contact with the leach solution.  This issue should be further addressed in the feasibility study.

Those that have been involved with McArthur River or Cigar Lake know that they are 50% mine/ 50% science project and it looks like the Phoenix deposit at Wheeler River is going to fit this bill also.  Beware of the Darcy’s.

I’ll go hide out in the base metal world for awhile.


  1. Standard Uranium, Palangana and Hobson NI 43-101, Nov. 2005 page 34.  www.sedar.com

Denison Mines Corp.,  Prefeasibility Study Report for the Wheeler River Uranium Project, September 24,2018  Filed October 30,2018 www.sedar.com


  1. Love the blog Doug. Thanks.

    Are you on twitter? I could not find you. Would be a great way to update us when you have a new post.

  2. I can't behave myself in chat rooms such as twitter so trust me, this is a better format for me. I would rather educate and bring up pertinent points here instead of insulting others and publicly questioning their credibility there. Keeping it facts based is better.


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