Provided below is the second part of an in-depth conversation with The Unknown Geologist on the geological model for the one-and-only Goldboro project owned by Anaconda Mining (TSX:ANX).
Peter Bell: These high-grade ore shoots within the belts are stacked, but the shoots aren't necessarily right next to each other within that stack right?
Unknown Geologist: That is correct Peter. At the Boston-Richardson, for example, we had ore shoots on both limbs of the anticline that projected to surface near the existing ramp. The Boston-Richardson belt itself is exposed in the ramp and there's high-grade material, about 6-7 grams per tonne gold, in the cross cut on the 125 level (suggesting another ore shoot below the one mined out). Down at the 250 level, chip samples from the Boston-Richardson run at about a 1.5 grams over a meter, which is lower grade (and outside the ore shoot).
You kind of have to get paper to pencil to understand these three-dimensional flexure zones, but you can see in the images that the whole Goldbor structure is folded and what I am talking about is a ripple that goes down each limb in a secondary wave pattern. Every time it flexes a certain way, it will potentially have an ore shoot. Each shoot is only about 20 meters high, so they're pretty small targets to hit will drill core.
Peter Bell: What does that mean, 20 meters high?
Unknown Geologist: 20 meters up and down the limb. The limbs go down on each side for, probably, kilometers since they are sedimentary units. Each belt extends away from the anticlinal axis down the slopes of the anticline for kilometers.
Peter Bell: Would you describe the gold as "pinching and swelling" within that?
Unknown Geologist: Not really. The fine grain argillite materials that are present because it’s a sedimentary unit of rock, and the quartz veins like to come in a certain way when it folded.
Peter Bell: And how does that fit with these 20-meter intervals on the belt?
Unknown Geologist: That is based on where the secondary flexure hits the anticline. Think of the anticline as the first phase of deformation, then there's another phase of deformation that put a flexure in a wave pattern down that limb.
There are so many holes drilled there with over 60 grams of gold per tonne, which I believe was the cap for high-grade intercepts in past resource models, and each of those is probably in an ore shoot. Once you line those high-grade intercepts up on each belt, you should start to see the ore shoot lineations. Another term for this is the ribbon model which was proven to be very effective in the large deposits in Australia.
Peter Bell: Okay, I think I’m getting it now.
Unknown Geologist: All of this relates to that high-grade hole Anaconda reported in 2017 with that intersection of 2,500 grams per tonne gold and 428 grams over 2.6 meters. That was a really nice intersection and it was only 38 meters deep! Anaconda knows which belt that was in and I asked them, "If you go down-dip at 25 degrees from that intersection in the same belt, do you have any other high-grade intersections?" They told me, "Yes, there is one but it's quite a ways out." I strongly encouraged them to draw a line between the two and drill a hole where that line intersects the belt because I believe they would hit another high-grade ore-shoot intersection.
Peter Bell: Really?
Unknown Geologist: Yes. There are so many belts and ore shoots that you can't possibly establish that they are all contiguous – you'd have to drill so many holes that it would be almost impossible to do so. If you drilled them as vertical holes at the right places, then you could get a lot of them quickly. Anyways, it's a nice problem to have but it's still a problem because it means you can't show contiguous units of high-grade gold mineralization in the resource model. Once you start mining this thing and understand the orientation of them, you'll be there for a long time is my guess.
Peter Bell: That was hole number 17-04 on East Goldbrook that you mentioned. With the 0.5-meter intercept, how does that compare with what you said about the shoots being 20 meters tall?
Unknown Geologist: Again, it's hard to describe without paper and pencil. If you look at the Boston-Richardson, for example, the ore shoots were not right on the nose of the anticline – they were down a bit from the nose of the anticline on the limbs. From the nose of the anticline down the south limb, it was probably 30 meters to the top of ore shoot and 50 meters to the bottom. Does that help?
Peter Bell: Yes, it does.
Unknown Geologist: And keep in mind that it all angles down to the east at 25 degrees.
Peter Bell: Right. Let me try to draw it. What you were just describing is something like this.
Unknown Geologist: Looks good. Keep in mind the scale of that map, too. Where you are drawing is 475 meters deep, so 20 meters is quite small. And that shows the problem of just how small they are.
Also, that’s only one belt. You can expect shoots on both limbs at Goldboro. And there is probably another one of them 50 meters up the limb! Do you see where that VG is on the third and the fourth holes? Yes, connect the dots.
Peter Bell: Oh, wow.
Unknown Geologist: A picture's worth a thousand words, Peter. That's kind of like what I see Goldboro to be.
Peter Bell: But this is where we get to the limits of what we know from the company’s reports.
Unknown Geologist: Right. We don't know which exactly which belts had the high-grade intercepts, but that’s the model.
The first picture on the website shows a few interesting things we can discuss here. Do you see the slices?
Peter Bell: Yes, I do.
Unknown Geologist: It's hard to see, but these belts show on surface just like you're drawing. It comes to surface and then plunges down to the east. There are at least 30 of these things, which is huge. And then there's the ramp and the Boston-Richardson Mine itself shown in green.
Peter Bell: Is this how do the shoots trace down the belts in this diagram?
Unknown Geologist: Yes. There is one ore shoot at surface, which goes down at 25 degrees, and then there's another about 50 meters down that limb.
The Boston-Richardson has been mined-out and there's an ore shoot on it that dips down in parallel to the nose of the anticline. The width of it is about the thickness of your line, which is very small on these diagrams.
Peter Bell: And do you have a sense for how long that shoot was on the Boston-Richardson?
Unknown Geologist: From surface all the way to the bottom.
Peter Bell: Really?
Unknown Geologist: Yes, indeed. 700 feet deep!
That is just one unit of the belt system that has been mined and it's right in the middle of it all. And there were ore shoots known on both limbs.
Peter Bell: Amazing to hear you say that the shoots went down from surface to the bottom of the mine. Do you know if the grade was fairly homogeneous across the length of it?
Unknown Geologist: I don't know, Peter. The historical documents showed it as a high-grade ore shoot that lined-up across the belt. They put a dashed line on the top and bottom of the shoot in the diagram and you can see all the stopes. I told Anaconda that they simply have to get a copy of that mine plan.
The other belts will likely look very similar to the Boston Richardson. And it gives details on the ribbon model that we are discussing here now, which they identified at Bendigo with these secondary flexures that open up dilation zones. It's just like a big wave went through the whole thing.
Waves on an ocean have a peak and trough, right? That peak is like the ore shoot and it extends down the limb of the whole belt.
Peter Bell: Wow. The orientation of all that is a bit surprising, but it makes sense intuitively. If I tried to draw one of these shoots off to the west, then it would look something like this? From surface running parallel to the saddle, all the way down the belt?
Unknown Geologist: Yes. And you see that spot you started your line at surface? Well, that would be a good place to start some bulk sampling. if you stripped the mineralized material off right there, then you would see really nice high grade. At least that's what they drew in the Boston Richardson.
And if you draw a line from the top of one ore shoot to top of the other ore shoot on the other limb of the anticline, then you hit the 123 Belt below it and VG occurrences with high arsenopyrite concentrations.
Peter Bell: Of course.
Unknown Geologist: It's tricky, but I think Anaconda understands it. I want to see their model to make sure. There's a model in the 43-101 that somewhat resembles what you're showing, but I want to understand how they drilled their holes.
You can see there's a lot of holes in the second image. It looks like there are over 15 holes in that small part of the deposit. There is no scale on the diagram, but it’s probably a hundred-meter grid. At that scale, you may only hit an ore shoot in one hole.
Peter Bell: Right. I don't see a lot of follow-up holes in this historical drilling here. Even if they hit it in this hole, say, they were not really chasing it.
Unknown Geologist: Exactly. I think you're getting it. This is what I'm telling Anaconda: Look at the holes that hit ore shoots and line them up with other holes along the same belt.
Please note that The Unknown Geologist, Mr. David Hatchette is affiliated with the company but he does not represent the company.