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Friday, October 18, 2019

Low Sulfidation Epithermal deposits

Low Sulfidation (LS) Epithermal drivel 

Just a quick intro on LS-Epithermal vein deposits. Very simple, but there is a reason for this....

911 metallurgist has a great description of low sulfidation epithernal deposits here - link, from which are some important things to note (in general) about low sulfidation (LS) Epithermal deposits and districts:
  • There are often multiple, generally, parallel veins

  • That are associated with (normal) faults. In many districts, often there are blind veins (i.e. the veins don't outcrop on surface).

  • Ore-grade mineralization in a district generally occurs over a specific range*
  • Mineralization isn't distributed equally throughout the vein, but is found in  specific zones (ore-shoots)


*assuming no post-mineral faulting (e.g. San Dimas) or multiple mineralizing/stacked events (e.g. very large epithermal districts e.g. Guanajuato, +/- Valdecanas).

For exploration it is key to target this favorable horizon, as if you
  • Drill above = erratic occasional Au-Ag hits (but could see elevated As, Hg and Sb).
  • Drill below = may hit elevated base metal (Pb, Zn, Cu) grades and low/no Au-Ag (e.g. San Sebastian - Hugh zone (Hecla Mining))

So when you are looking at a company with LS-Epithermal projects you want to see:
  1. Land position - you want the company to control or have a good chunk of a district. There is no point getting to excited about a company with a small project as any decent mineralization will quickly leave the property.
  2. More veins = more potential for large tonnages and multiple ore-shoots (e.g. Las Chispas).
  3. Large vertical extent of high-grade mineralization - this is harder without drilling. Generally in LS-Epithermal deposits the bonanza zone is ~200m thick (bigger systems = larger vertical extents - Santo Nino vein, Fresnillo had a 3-400m vertical extent).

References:
Rhys, D el al  (2017) - Gold’17 – February 2017 – Rotorua, New Zealand 82  l Structure of the Palmarejo Mining District

Friday, September 13, 2019

Quick GGI update

PR from yesterday from Garibaldi (link), and I've updated the Leapfrog model with the results form holes 47 and 53 (link)

now some piccies

Hole 48

This is an infill hole, it is 16m from holes EL-17-09 and 10 and 10m from holes EL-17-14



However, the when we look at the lauded 44.5m at 1.2% Ni and 0.8% Cu we quickly see in reality this wide zone is really running ~0.5% Ni and Cu with the majority of the metals in the ~5m wide massive sulfide zone.


Hole 53



What we predicted, again, the massive sulfide zone was slightly wider than I had doodled in an earlier post.

How do this change the lower zone massive sulfide footprint?

a bunion
Not by much.

So how big is Nickel mountain? Here is my modeled Ni mineralization



Which gives me an approximate size of...



As people got butt-hurt about me comparing Nickel Mountain with Voisey's Bay, here it is compared to a multitude of Nickel deposits (source - link).





So, it isn't, what you would call a tier-1 deposit

Saturday, September 7, 2019

Canadian Topo Maps

Totally irrelevant post, but if you need reasonable topo maps for Canada, the Government of Canada have a great Google Earth link to their Digital elevation models

250K maps (link)



50K maps (link)

even cartographers don't give a shit about the Canadian Arctic
I've found that the best way to download the files is to right-click on the hyperlink and copy and paste it into your browser

Me, working on the Shovelnose property, with my reputation....
This will download a geotiff file for the area selected.

very cool

Thursday, August 22, 2019

Garibaldi - attack of the biscuits

Sorry for my tardiness, I was playing around with copper deposits.

We got a PR from our chums at Garibaldi Resources announcing the first of many few drill results from Nickel Mountain (link)

To the surprise of no-one, we didn’t get any decent maps with this PR, just a couple that re hard to read at the bottom of the PR - I couldn’t see where these new holes were located , could you?

but fear ye not, here they are....

OMG!!!!! both of them have targeted the Swiss Cheese Discovery Zone.

Let’s look at the holes in a bit more detail

Hole EL-19-47

This is drilling the eastern continuation of the lower discovery zone.

That hole was drilled a massive 15m from hole EL-18-16 and 24m from the massive sulfide hit in hole EL-18-24. Not really a massive leap of faith that would add millions and millions of tonnes to the deposit.

EL-19-53

This hole was drilled from the same platform as hole 47 but in a different direction, plunging into the heart of the known


Just 11.3m from the massive sulfides hit in hole EL-18-22


And 14.3m from the massive sulfides in hole EL-18-20…

Warning: the following image contains an “interpretation” involving one or more squiggly lines and maybe words, but definitely no numbers. Please sit down!


What is cool, is that you can join up the massive sulfide hits in several holes to work out an approximate outline of the Discovery Zone.

Isometric view looking SW. Red outline is my interpreted limit to sulfide mineralization
In Plan view, with some annotations and a scale



I added the 10m buffers around the drill-holes as it allows you to quickly see areas they haven't been drilled. 

A lot (20) of holes have penetrated the lower discovery zone defining a zone of massive sulfides that:
  • Dimensions of ~125m long, 15-35m wide and 5-10m thick (true thickness)
  • Or an approximate volume of 23,500 cubic meters
  • Or an approximate tonnage of 108,000 tonnes (using an SG of 4.6*)
*SG of Pentlandite (main Ni sulfide) is 4.6 to 5.0; Chalcopyrite (copper sulfide) is 4.1 to 4.3

So, Nickel Mountains isn't big, but there are a few areas where mineralization can be expanded

dashed green outlines - where mineralization appears to be open


Summary


Nothing new, just a couple of holes pushing the boundaries of mineralization by a metaphorical duck’s fart, and just for fun, here is the Nickel Mountain deposit compared to that tiddler, Voisey’s Bay.


Leapfrog viewer file can be downloaded from here

Friday, August 16, 2019

Cu Acquisitions

I had a chuckle at Cordoba’s PR (link) on their resources, it is quite small, and spread over several deposits, but it made me think….

How good does a porphyry copper deposit need to be to give a massive erection to a mining executive and make them splash their wodge to buy it?

Fortunately, Oroco Resources had included a nice slide in their presentation (link), that I was able to use.

Assumptions:
  • CuEq derived from Cu and Au, the other metals don’t generate much value
  • 100% recovery
  • Metal prices of:
    • Cu = US$2.50/lb
    • Au = US$1250/oz
    • Ag = no-one gives a shit about this
Magenta = San Matias
Quite a spread, please note that I haven’t separated producing mines from development projects, and many of the largest deposits will have a high-grade core/starter pit (e.g. Cobre Panama), but you can clearly see that all bar one (El Pilar in Mexico) contained >1Mt copper.

So, plot on your favorite Cu project to see where it is, as companies don't appear to be very choosy with what they buy,.

In my opinion, we can see that lots of these projects are too low grade (<0.5% Cu) for development, but it seems that the only thing that matters is size.

I’m sure it is more technical than that, but it is an interesting guide to have a look to see is out there, and when copper starts raging, the FOMO will be strong and lots of stupid strategic acquisitions will be made and hopefully you’ll make out like bandits.

Monday, July 8, 2019

Pause

Sorry for the lack of posts, I've been working on a large project that has been consuming all of my time.

It is now complete-ish, so I have some time to waste on this blog!

Buritica - Narrow veins and potential issues

Continental Gold have been releasing some juicy assay data from Buritic√°, here is an example from last month (link).


I hate companies that report strike length samples, to me they are trying to deceive you into misreading the table and believing that they have wide zones of gold mineralization:
  • e.g. 31m @ 24.09 g/t Au and 76.22 g/t Ag at 2.26m width
translates to:
  • A series of samples taken from a vein where a 31m long portion averaged 24.09 g/t Au and 7.66 g/t Ag over an average width of 2.26m 

However, what interested me most about this PR were the maps and this statement:


In Summary:
  • No capping
  • Weighted averages
  • No dilution
The issue with no using capping and using a weighted average is that a few high-grade samples can increase the overall average of the mineralized zone lead to companies calculating resource blocks with higher grades than actually occur. This is especially problematic this methodology continues through to mine development (this often happens when companies do resource calculations internally), when they get into a situation where reserve/resource grades >> mined grades (e.g. several mines operated by First Majestic).

I’m using the maps from the March 9th PR (link) as they give a breakdown for each channel sample compared to just a series of colored rectangles used in later PRs.


We’ll focus on the areas YR_1444_CX05 - Stope Areas 1 and 2 – I’ve added a grade legend as the one on the original maps is quite hard to read.


We know that Continental plan to mine all of this vein in this area as they have them shown as potential stopes, but if you look closely at this map you see 2 things:

1. Grade

The average weighted, uncapped grade for this area = 16.95 g/t Au, or red according to the grade legend, so:
  • How many samples are red (or better) from this section?
    • 7 out of 26 or 27% assayed >10 g/t Au or
    • 73% of the channel samples assayed less than 10 g/t Au
In high-grade gold mine you get a lot of variability, but it would be reasonable to expect that the modal value would be close to the reported average grade of this area? Let us look closer at the map.

At the far west end of the “2” stope area, we see an ultra-high-grade sample (cyan rectangle) that is grading 2.26m @ 119.6 g/t Au, what would happen to the average grade for the entire block if we remove this sample?
    • Grade drops from 16.95 g/t Au to 9.11 g/t Au, or by 46%
Typically mining companies cap ultra-high-grade samples to avoid this issue, where a couple of high-grade samples can significantly increase the overall grade of a zone, we'll do the same here:
  • Uncapped – 2.23m @ 16.95 g/t Au over a 78m strike length
  • 50 g/t Au Cap – 2.23m @ 11.08 g/t Au – a 35% reduction
  • 30 g/t Au Cap – 2.23m @ 9.72 g/t Au – a 43% reduction
A ‘traditional’ way that resources were calculated in underground mines (some mines still use this method (link)), is that they extended the mineralization above and below the level by a distance equal to half-strike length, so for this area we can guesstimate the contained gold for the 2 stopes and see the impact of applying a cap:

Assumptions
  • Strike length = 78m
  • Vertical extent = 78m (39m above and 39m below the level)
  • Average width = 2.23m
  • Tonnage factor/specific gravity = 3.13 t/m3 (from 2019 technical report – table 11.1)

Guesstimate contained gold:
  • Uncapped = 21,150 oz
  • 50 g/t Au cap = contained ounces drop to 15,128 oz
  • 30 g/t Au Cap = Au decreases to 12,273 oz Au
Just applying a small cap, we've reduced the average grade and therefore the contained gold by a lot.

You can clearly see the impact that a few high-grade samples can have! This is why companies apply a cap, it makes the results less sexy, but is important, as if you don't, you can start to include a lot of waste with the ore and it works it way into the mine plan, which looks like it is happening here as we can see that the limits of the stopes (the black lines) include everything, including marginal (yellow) and waste (green, grey and white) portions of the vein.

Essentially, based on the channel samples gold grade distribution in the stope is more like this:
















We have some narrow high-grade zones (red), a large waste zone in the middle (green) and the majority of the block is low grade (orange) or marginal (yellow), which is <<16.95 g/t Au as originally advertised in the PR.

Why is this an issue? We can see that using a weighted average can skew the grade significantly (in this case by up to 40%), and in several mines that I know, they continue to use this 'traditional method' to define resources and zones to be mined.

A couple of high-grade samples/drill-holes can quickly add a chunk of mathematical resources that are have significantly higher grades than reality leading to large ares of sub-economic or marginal blocks being included in the resources and eventually mined.

This results in lower than expected head grades, lower gold production, lower revenues, higher per ounce production costs and reduced profits.

These are all things that shareholders love.

How many mines do you know where grades haven't met expectations or feasibility studies?

2. Vein widths

One thing that I found amusing was that all the samples thicknesses range from 2.06 to 2.27m. Remarkably consistent!

However, when you look at the level plans, you see:


That the vein is represented by a very thin red line, that is significantly narrower than the channel sample rectangles. That is the vein...

Here is a photo from the Fire Creek Mine in Nevada. 


See how they are not just sampling the vein, but the surrounding country rock (this is standard practice, you want to know the grade of everything you will be mining). In this photo the vein is ~90cm wide, and we can see that they are sampling ~1.5m either side of the vein, or a total channel sample width of ~3m. We can also see that a separate sample was taken from the small vein on the left. This is standard sampling practice.

So, if Continental are doing something similar, we would expect that they are sampling the vein, and 1m either side, which indicates that the vein is actually 5-27cm wide, which is similar to the drilled vein thicknesses (link).




High-grade but narrow, with a bit of gold in the country rock around the vein

Why is this an issue? Well in narrow vein mines, controlling dilution is critical, if you have excessive dilution, you will have:
  • difficulty in maintaining a consistent head-grade
  • difficulty in using modern mining equipment
  • low production rates
You can use highly selective mining methods (e.g. Resue (link)), but they have low production rates. You can increase production by either using mechanized methods (increase dilution), or extracting ore from many heading (increased labor costs)

If you have a large mill, you need to mine a lot of material and therefore you can't be very selective be very selective. At Buritica, the mining width (based on the width of the mine level) appears to be ~2.5m, whereas the the vein widths (in this section of the mine)  around 0.25m, so you already have massive dilution.

Minor changes in thickness of the vein or the inability to minimize mining widths and therefore minimize dilution can cascade through an operation, significantly impacting mine production and profitability.

How many mines have you read about that have had issues with grade control, or throughput?

We've see with Pretium at Brucejack where initial resource and reserve calculations appear to have struggled with accurately re-conciliating head-grades to estimated reserve/resource grades, that led to them implement a new comprehensive grade control program (with associated costs) to try and better understand the gold distribution.

I'm not saying that the same is happening at Buritic√°, but history rhymes, we have a situation where a company wants to mine a series of narrow, high-grade veins and some of the PRs (obviosuly promotional in the way that the data is shows) appears to suggest that several areas could have significantly different grades as thought.

As we have seen at Brucejack (and several other underground mines), there is a desire to define as large a resource as possible, and as quickly as possible, which can lead to the situation where mine plans, scale of mining, are being advanced before the true nature of gold distribution in the veins is properly understood.