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Monday, January 2, 2017

Hermosa Beauty pageant - Swimsuit section

There has been a lot of news about Arizona Mining's Hermosa Central Taylor deposit. The funny thing is, most of it is self-inflicted, if they had spent a bit more time thinking about what they were doing and (the hardest of all) why*.

*Just me making a naive comment - I try to think about the possible end game for a project (sell or develop) whereas most exploration companies are just interested in the short-term gain.

I'm going to take you through the Taylor beauty show, but first my disclaimer.

The 3D model of the drilling data is not very accurate, because:
  • Hole locations have been sourced from technical report and also digitized from plan maps provided in press releases (accuracy +/- 30m).
  • No dip, dip direction or hole depths have been provided and this has been estimated from plan maps accompanying the press releases.
  • No hole deviation - drill-holes bend slightly, the longer the hole the more bent it becomes (deviation). I haven't included hole deviation in the model as it is never included in PRs.
  • No hole depths - I've used deepest reported interval +200m 
You can download the 3-D model from here (link).

I've split this post up into several section (I'll publish one per day), so that people aren't overwhelmed by a massive post containing everything.

Geology-wank

The Taylor deposit is continuation of the Hermosa/Central silver-manganese oxide (manto oxide) mineralization to depth. There is no clever exploration here, Arizona Mining just been following the manto down dip to nearly 1 km depths.

Central = pink; Taylor = yellow

So - Taylor and Central are different names for different parts of the same deposit.

Swimsuit section - Recent drill results

There have been a flurry of press releases announcing some fairly spectacular drill-results (link and link).We can see that the majority of the mineralization is in CRD (Carbonate replacement deposits) with a few veins scattered around the project. So the veins intersected by hole 359, 386 and 386 give some nice numbers and are interesting locally, but in the big scheme are irrelevant.

not many veins.. Red = Dec 15 DH, Green = Dec 21 DH
Hole 359 is a classic case of what happens when an almost vertical hole hits a vertical veins - a massive core intercept from a vein that is probably only 1-2m wide. So, the veins are irrelevant (except for PR headlines). If you look more closely at hole 359, you would expect it to hit the main Taylor deposit at around 1,250m depth, so why did they release the assays before the hole got to the main mineralized zone, did something scare them......

There are some very nice hits, but we do see a lot of grade smearing from narrower high grade zones over wider thicknesses, which suggest that only a part of the Taylor zone is strongly mineralized. For example:

  • HDS-353 - 9.8m @ 8.19% Pb, 12.21% Zn inc. 5.2m @ 14.75% Pb, 22.04% Zn
    • residual grade 4.6m @ 0.77% Pb, 1.1% Zn
  • HDS-382 - 27.4m @ 2.07% Pb, 1.06% Zn, inc. 8.2m @ 4.12% Pb, 2.39% Zn
    • residual grade = 19.2m @ 1.19% Pb, 0.9% Zn
  • HDS-387 - 34.3m @ 9.56% Pb, 5.41% Zn inc. 12.6m @ 21.84% Pb, 11.12% Zn
    • residual grade = 21.7m @ 2.43% Pb, 2.1% Zn

We see this repeatedly, is this the same for all the thick intercepts? Is Taylor really just a 5m zone of economic mineralization (albeit at 10+% Pb+Zn) surrounded by sub-economic country rocks? There isn't enough data to say.

Here is a long section through the deposit.

blue line = TAG's BS ore zones.
I've drawn a series of blue lines showing my guesstimate ore horizons. You can see that the mineralization is getting very deep to the left (NW), and there isn't really much point drilling out there, you'll get some reasonable hits, but you'll never mine it, just ask BHP-Rio how much a 1km deep shaft costs to excavate in Arizona....

I've also drawn a couple of red circles around some exceptionally thick intercepts. You can clearly see that they are different, hey are much thicker than the mineralized zones in adjacent holes.

I think that this is an impact of maybe syn or pre-mineral (basically faulting before or at the same time as mineralization occurred) faulting, with the mineralizing fluids using and replacing the fault zone, forming much thicker, but not very wide, vertical pipe(s) of mineralization. If that is the case, you would expect them to be modeled a bit differently in the resource model.


Exploration Upside

Short version - good

There are a few areas where the current resources can be expanded

black line = slide through the main Taylor body
red = 100m radius around dill-holes (indicated resources), blue = 200m radius (approx. limits for inferred resources)
You can see that the depoist is open to the NW (upper right) and also to the NE and SW, and regionally the project that covers a number of historic base metal mines.

red star = old mine
and a number of high-grade veins (map below).
veins, lots of lovely veins
but unfortunately, it looks like every silver lining has a black cloud!


part 2 tomorrow