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Wednesday, March 21, 2018

Deposit data

The USGS publish a lot of free data on mineral deposits through their open file reports. These reports often include the source data and spreadsheets.

Generic link -

Deposit specific links

  • Porphyry deposits - link and an older version link 
  • Sediment hosted Cu deposits - link
  • Sediment hosted Zinc deposits - link
  • Sediment hosted Au deposits - link
  • VMS - link

Please note that these reports aren't produced every year, so the data will be a bit out of date (up to 10 years depending on the deposit type).

As this post is very boring, here are some boobies

A beautiful pair of Boobies

Mineral deposits - a summary

Asiamet - Beutong

Asiamet have released a flurry of press releases this month, they've raised money (link) and recommenced drilling on the Beutong porphyry Cu-Au deposit (link).

It contains a decent amount of metal:

Or a global resource of 511Mt @ 0.48% Cu and 0.13 g/t Au or 0.56% CuEq.

If we plot them on the USGS chart of doom, we can see if Beutong is good enough to tickle the hairy balls of a major mining company?

Note: the log scale to the axes
Nope, at the moment it is nothing more than a friendly caress and a slight squeeze.

So what do Asiamet need to do to get it into the top right corner of the chart - the Acquisition Zone? To grab a major by the short and curlies, they'll need to:
  • Double the resource but keep it at the same grade - 1Bt @ 0.56% CuEq
  • Increase the grade, but keep the tonnage the same - ~500Mt @ 0.6% CuEq
To do this, they need to drill, but are there any obvious area where they can start?

I compiled the summary drill-hole data for Beutong - leapfrog model is here - link). Resources have been defined in 3 main areas.

East Porphyry

If we look at a plan map, we can see that the best intercepts all of the >0.5% Cu have come from the small (350m x 150m) quartz-stockwork. There is minor mineralization (<0.3% CuEq) in the host sedimentary units (grey). To the east sits an unmineralized (post-mineral) breccia. There is a small high-grade core, but this has been closed off (i.e. drilling has defined it limits with no obvious areas for expansion).

red line = surface outline of the stockwork zone
Looking at a section through the East Porphyry, we can see the stockwork is narrow (200-300m wide) but a few drill-holes (e.g. hole BEU0800D01 - 293m @ 0.6% Cu and 0.11 g/t Au starting at ~450m depth) have intersected >0.5% Cu mineralization to ~700m depths.

The skarn zone sits to the north - left
This deep continuation of mineralization hasn't been fully explored and with some targeted, long drill-holes will add some tonnage to the East Porphyry resources.

The question is, will anyone care that most of the potentially resources will be at >400m depth and probably beyond the limits for an open pit mine, and too small and low grade for a block cave?

West Porphyry

There has been much less drilling on the Western Porphyry zone, but the results are generally poorer than at the East Porphyry. Some 'round the world' drilling (holes going in every compass direction) have moderate intervals of generally low grade (>0.5% Cu and minor Au).

Green circles - areas where drilling has intersected >0.5% Cu
However, there are a couple of areas where drilling hit some moderate zones of >0.5% Cu that need follow-up drilling to see if they are part of something more substantial or just some lucky hits.


A small skarn zone is found just north of the East Porphyry. Its given some great hits - e.g. BC007-01 - 48m @ 1.63% Cu and 0.88\ g/t Au.

getting worse with depth

However, it look like we have some supergene enrichment (link - a very complicated presentation , but slide 20 is a good). With higher Cu grades close to surface and grades decreasing with depth.


Even tough there are some areas where the current resources can be added to, I don't think that there is enough in the current resource areas to make the project enticing enough for a major.

For me, I believe that Asiamet need to find something new. We know that porphyries tend to occur in clusters, and, if they have not already done so, a decent portion of the 2018 exploration budget should be used for regional exploration to find some new targets.

Friday, March 16, 2018

Porphyry preamble

Ahh porphyries, conjuring vision of untold riches hidden in the bleak hills of the Andes or the mosquito infested jungles of Indonesia and Colombia.

However, ignoring the BS that explo-cos spout about their project being great because in reality, most aren't.

The CAPEX for a decent sized porphyry (or any large scale mine) typically run into the billions. No junior company can ever develop them, and so the best that they can do is entice a major to fund the project beyond the resource drilling stage.

However, ignoring the FOMO-mania that happens when metal prices go crazy, in general, most mining companies like to focus on projects that can support a minimum production profile, for example:
  • 100,000 tonnes of copper or 100,000 ounces of gold a year for >10 years
The idea is that the project will pay back the CAPEX (a novel idea), produce lots of cash for many years.

Here is a nice chart from the USGS (link) that displaying CuEq% grade vs tonnage for various copper deposits. Porphyries sit towards the large but low grade end of the spectrum. I've added some annotations and some well known projects.

blue crosses = porphyry projects

Remember: this chart uses the total resources for a project. Many projects have a high-grade core or are a combination of heap leach oxide and higher grade sulfide ores (with economics and cut-offs).

Smaller and/or lower grade projects do get developed, but often they are brownfield projects adjacent to an operation that mined a neighboring higher grade deposit.

What you want is:

  • A project that is in the top right part of the chart = takeover target 
  • An exploration stage project that shows the potential to get into the top right area.
What you want to look for are projects that are a decent size >200Mt and a reasonable grade - around 0.6% CuEq or >1 g/t AuEq, or show the potential to get there.

However, grade and tonnes aren't the only factors that impact a project's economics, but it is a good starting point.

Wednesday, February 28, 2018

Pretium - everything is great

Good news, Pretium at the BMO Conference is telling us that everything is great (link), no need to worry. Production at Brucejack is swell, and everything is going to be super-good after the mill expansion. For fun, they are looking for the source porphyry, because, why not.

We also got the Brucejack ramp up production figures, you know, the ones where grade and ounces produced went down. We actually get to see the 'official' head-grades, and they were worse than Otto calculated (link).

Tonnes up, production down - Pretium going for the win!

They also included a nice long section of the Brucejack block model, which was interesting.

The reserves aren't nice and consistent, there are distinct area of high and low mineralization, but there is an awful lot of the Proven Reserve blocks that are green and yellow (i.e. 5-10 g/t Au).

This isn't uncommon, but if Pretium want to maintain consistent production level, they'll need to be very good at balancing the production from high and low grade areas (mine scheduling), and for me, the erratic nature of the mineralization is the reason why Pretium gave such a huge range for the H1, 2018 production. They just can't quite nail down the grades.

TL:DR version - it is going to be hard to consistently maintain a head-grade at 14.5 g/t Au.

I apologize for the next section, it contains a very naughty word. If you are sensitive, please go here (link)

It would have been interesting to have seen a a slide on reconciliation to see why they had missed their targets, was it due to:
  • Poor reconciliation - mined graded not equaling reserve grade
  • Slow development - unable to access proposed 2017 production areas and forced to mine peripheral, low grade zones.
We all know it is grade reconciliation, hence the reason they are doing a new grade control program and drilling the stopes on 5-7m centers. However, the slide that concerned me the most was this one (slide 17)

According to Paths, Pretium are retards, and are actually using the Reserve figures in their own technical reports (who the feck does that?!?), and are projecting that after the mill is expanded, the 2019 production will be:
  • ~580,000 oz Au per year 
  • A head grade at the Reserve Grade - 14.5 g/t Au*
  • AISC @ ~$570/ounce
*if you plug the numbers into excel you get a recoverable grade of 13.2 g/t Au or a recovery rate of 91%

So, to do this, all they need to do is solve the grade control issues, improve mine scheduling, improve recovery, and increase the underground development. Nice and easy.

If they don't manage this, at 3,800 tonnes per day each 1 g/t decrease in head-grade means a drop in production by 44,000 ounces, or $57M decrease in revenues. That is a lot of money, especially if you want to do this:

Monday, February 26, 2018

Alacran - Sting of the Scorpion

PDAC season is in full flow, and lots of companies are pushing out press releases to telling us that they are great, everything is going super-well and please don't ignore us and sell our stock as we have no real news.

One of my favorite pig in lipstick press releases was from Cordoba Minerals (link), not only announcing an updated resource for Alacran, but telling us that theyz got cobalt az well, m8.

Fuk uz Forst Cobalt

We'll ignore that and look at the resources.

Original, Jan 2017 resources

hard to read, but resources calculated at $1300/oz Au and $2.50/lb Cu

New and improved resources:

@ $1400/oz Au and $3.15/lb Cu

I liked the interesting metal prices used, Cordoba was a little generous with the gold price, but why don't we do some maths and see how the project has grown with another successful year of exploration.

I mean, look at that, they increased resources by ~27%. That deserves a good hug and a nice pat on the back, we'll ignore the fact that as the tonnes have increased, those nasty little copper and gold atoms have been efficient with their New Year resolutions. Those pricks have been on a diet!

and given the deposit a stunningly unimpressive negative increase in contained metals.

  • Copper 
    • Grades dropped by 22%
    • contained metal stayed essentially the same
  • Gold
    • Grades dropped by 32%
    • contained gold dropped by 15% or 94,000 ounces
So, basically you've made Alacran worse. Well done!

Friday, February 16, 2018

GT Gold - don't sniff the Saddle

GT Gold Corp's saddle deposit was causing a lot of excitement last year and have recently announced some decent new results (link and link).


  • Drilling has defined a small, moderate grade deposit.
  • Moderate expansion potential:
    • South Zone: partially open to the East and West
    • North Zone - TTD057 hit good values, but surface Au samples suggest that this zone is small.
    • Porphyry mineralization in hole TTD062 is interesting, but not economic. Highest grade zone appear to be restricted to narrow zones (dykes?).
  • Decent Au recoveries from initial metallurgical studies.
I was pleasantly surprised that GT gold include a full breakdown of the DH assays (link) on their website, and as this is a new project for me I want to look at 3 areas:
  1. Size
  2. Upside
  3. Potential problems
For your viewing pleasure, you can download the Leapfrog viewer file from here (link). Please note, I haven't found the RC collar information, so they are not included.


I did my normal thing, brought in the assays, had a look at the data to see if there were any trends confirm GT Gold's interpretations, that gold occurs in a series of steeply dipping veins.
Green arrow = mineralization plunge

I used this trend to create a series of grade shells.

To calculate a guesstimate of contained gold.

It looks like GT Gold have defined a small, but moderate grade resource. How can they make it bigger?


I want to see how easily GT Gold can expand the gold mineralization. So I decided to compare the drilled gold zones against the prospect-wide soil sampling maps found in the 2016 technical report.


Au DH assays and Au in soil


Au DH assays and As in soil
We can see that surface gold and arsenic correlate well with the gold mineralization hit by the drilling. You can also see that the 2 large soil anomalies haven't been completely drilled.

South Saddle

proposed hole = cyan lines
The South Saddle Zone has been well drilled, but we can see that the Au soil anomaly continues for another 300m to the NW. We can also see that hole TTD051 missed, at GT gold should drill a hole (highlighted) from this platform to the NE to check for the continuation of the multiple Au zones hit in drill-hole TTD053

We also see a partially tested anomaly ~250m to the East. Drill hole TTD059 hit several >1g/t Au structures and a few holes between this hole and TTD028 will test the continuation of the main South Saddle deposit to the east.

GT may also want to drill a DH to the N from the platform of hole TTD061 to test another small Au soil anomaly to see if these three zones link up.

North Saddle

The North Saddle gold anomaly is virtually untested, and is 400m long and ~250m wide. The anomaly does appear to be following a drainage and may just be an erosion anomaly, but drill-hole TTD057 hit multiple >1g/t Au structures along the eastern edge of this anomaly and a couple more holes should be drilled to see if there is anything bigger to find in the area.


Hole TTD062 hit some weakly mineralized porphyry (210m @ 0.16% Cu and 0.14 g/t Au - i.e. waste) and the hole was drilled into the center of the large magnetic anomaly, so it it doesn't look like it will turn into anything.

Magenta = magnetic high


The 2016 technical report does discuss additional targets, I've been happy to see that there is good correlation between soil Au and As and drilled mineralization, and maybe a good step would be to expand the soil sampling program across the project, and if GT gold want to save a few bucks (and get quicker results), they could use a pXRF on the soil samples and map out the Arsenic as a proxy for gold distribution.


We got a Valentine's gift from GT (link) with some initial metallurgical results. I quickly checked Head grade against recovery to make sure that GT tested material with different head-grades (it is common for companies to only test the 'best' material which can skew the results).

We see a nice range of head-grades from low to high, and the recoveries are sitting nicely around the 80% level. I didn't see anything in the text to explain why 2 composites had 0% recovery, it would have been nice to have had a bit of text explaining why. It would have been nice to have seen a summary of ore type (oxide, mixed and sulfide - if it is important) and maybe where the samples had come from, but these are minor niggles.

I've created a new view showing the location of the Cu assays in the DH data (link)


GT gold have defined a small, moderate grade gold deposit. There is reasonable expansion potential laterally, the depth extents to the South Saddle appear to be well drilled), and my gut-feel max size for Saddle/Saddle north is sitting around ~1Moz @1 g/t.

The metallurgical studies are positive, and appear to minimize any potential impact that the elevated As could have had on the deposit.

However, I can't see, from the data presented, how GT will significantly expand the project to a size where larger companies would be looking at acquiring it (say around 2Moz). Maybe with some regional exploration, several additional gold zones could be defined for drilling later on this year.

The porphyry potential, albeit from a single hole, seems to be minimal.