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Wednesday, May 25, 2016

Sandy, can't you see I'm in misery?

CORRECTION: I had used the incorrect datum for the drilling and images. I've uploaded corrected Leapfrog views and corrected the BS resource calculation and images.

Orex have released some more drill results today, so here is a quick-ish update.

The TL:DR version (so you don’t have to read everything).

  • New drilling has focused on expanding the known mineralisation.
  • Assays continue to support the idea that there are 2 styles of silver mineralisation at Sandra.
    • A high grade, vertical zones associated with veining and/or faulting
    • A low grade zone of disseminated mineralisation
  • Low grade zones don’t appear to be very extensive (~150m)
  • high-grade zones don't appear to be very continuous along strike.
  • Drilling in the far SE and NW only cut thin, low grade silver, hinting the system is dying out in these directions.
  • TAG Bote* resource estimation: 11.4MT @ 137 g/t Ag for ~51Moz Ag – let’s see how close I am! 
  • this changes to ~46Moz Ag if we use an SG of 2.3

Just my BS calculation,

 *Back of the envelope: The resource calculation is complete BS, I’ve just calculated the average grade and volume for each grade shell, used an S.G. of 2.6 (I’ve assumed that the rhyolites are slightly porous) and then added the number together, so nothing fancy or professional but I’m interested to see how close I get. Spreadsheet link here.

Questions

  • Why hasn’t there been any follow-up around drill-holes SA-15-001 and 002), where the best grades were intersected?
  • Are their enough high grade zones to define a decent high grade resource?
  • When will Orex send some samples for metallurgical testing? Sorry to keep going on about this, but for this deposit, it needs to be demonstrated that the silver can be recovered.
I've put the new data into updated Leapfrog viewer files can be found:
  • small version (link) - 3MB
  • large version (link) - has topography and satellite image - 105MB



Drilling has focused on expanding the known mineralisation. Results aren't ground breaking, they continue to show similar results to earlier drill-holes, that they are intersecting narrow-ish, vertical zones high grade mineralisation surrounded by halo of low to moderate grade disseminated mineralisation.
May 24th holes are red, and holes have been colored by the PR data


Cross section through Sandra highlighting the narrow high-grade zones and the surrounding low-grade disseminated mineralisation. We see that there are multiple, parallel high grade zones.

Here we can see the variability of the silver grades over short distances. Hole 09 intersected a relatively thick zone of mineralisation that is much lower grade in the adjacent (15m distance) drill-holes 10 and 26)



Drill-holes 28 and 29 were drilled 250m northwest from holes 16 and 17 (Cerro Chato zone), where they hit a very narrow zone of fairly average mineralisation. this suggests that the system is becoming weaker, as we move away from the core zone around drill-holes 01 and 02.
Here we have a long section (looking south) with the drill-holes and my grade shells



Mineralization is pinching out to the East (holes 28 and 29) and is eroded away to the west

Cross section (looking west), do we also see a slight thinning of the silver zone to the south?

Plan map showing trace of long section (yellow) and cross section (cyan)

Conclusions

To me, from the data in the Public domain, the drilling has intersected several parallel vertical silver bearing structures/veining, that has a relatively extensive (up to 100m?) halo of weak to moderate disseminated mineralisation.
What is intriguing geologically, is that the drilling doesn't appear to show much (any?) mineralisation outside of this rhyolite unit.
Why? Could we have a situation where the disseminated silver in the rhyolites is related to a early mineralising event, and the veining is later and has remobilised and concentrated the silver into the vertical veins.
However, it is more likely that the current drilling has focused on defining the limits of the disseminated mineralisation and they haven't drilled any deeper holes to see if the high grade zones continue to depth.

This is what I think is happening at Sandra.
high grade in the veins, with silver 'leaking' into the porous rhyolite unit.